Bantor:
Congratulatons on obtaining your first real camera - a real gem!!!
1. Your camera, like many other SLRs, are designed so that the widest aperature is used for focusing, composing, exposure measuring, etc.. The aperature will only close down once the shutter button is pushed.
While all of this is advantageous, there are also some disadvantages - namely, (1) users of SLR cameras will never see the picture they really take if their eyes are looking through the viewfinder, since the mirror moves up to allow light transmission through the lens to the film and thus blocks viewing of the image - first - prior to the aperature closing down to the chosen F/stop and (2) all of this preliminary processes causes a small time delay between the time you press the shutter release button and the photograph is actually taken.
For that reason, users of SLR cameras usually have to "anticipate" the action, expression, status, etc. of their subject. For example, in shooting a car or horse race, you might find yourself pushing the button just slightly before the subject reaches a designated point rather than when they have arrived at that point.
A great deal of practice will get you into the ball park.
As an aside, a rangefinder camera, such as a Leica, etc., will allow you to see the subject at all times and because there is no mirror to move up and out of the way and because there is no need to stop the aperture blades down, the time response between shutter pushing and actual release is noticeably shorter.
2. The Canon FD lenses are designed to also close down manually so that they can be used on non-automatic extension tubes and/or on the Canon bellows with or without extension tubes. You'll have to consult your camera's manual to find out how this is accomplished. However, there is no need to set the lens aperature on manual operation unless you wish to "play" with the process and/or make use of non-automatic extension tubes or the bellows.
At this point, you might wish to explore the link below and bookmark it for future reference. As you scroll down, you'll even find information on an array of Canon cameras as well. Excellent source of information!!!
http://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/
3. Pushing the depth of field preview button doesn't really accomplish much since the restriction of light also affects your ability to see what's happening in the viewfinder.
Aside from making use of the depth of field scales on your lens, a much better suggestion is to look for an older book on photography, such as
The Honeywell Pentax Way or
The Pentax Way by Keppler or
The Leica Way by Matheson. I'm sure that there might be a similar title for Canon cameras of the same vintage - late 1960 through the early 1980's, but I don't remember its title. These references would be very useful if and when you begin to explore the world of photomacrography.
At any rate, at the back of each of the above titles are comprehensive depth of field tables, which are much easier to consult when you need to know such things. I have the
The Leica Way by Matheson - because I also have a Leica M-4 rangefinder along with my wife's Canon AE-1 and my Canon A-1.
4. For an excellent and very illustrative book on the basics of photography, I would highly recommend the reading and/or purchase of Charles Swedlund's book:
Photography: A Handbook of History, Materials, and Processes. This book can be found at your public library or through their inter-library loan system or through the link pasted below. Since you're beginning your photographic endeavors, I would - again - highly recommend - its purchase. You'll find a number of inexpensive paperback editions in good condition at the site below.
Look for and select a 1974 edition in good condition.
http://www.alibris.com/search/search.cfm?qwork=5111044&wauth=swedlund&wtit=Photography&matches=72&qsort=r&cm_re=works*listing*title
If my memory serves me correctly, Swedlund was a professor of photography at Southern Illinois University and was probably responsible for the sponsorship of the two day Leica Photographic Seminar that I attended there many years ago.
The above suggested book also has an excellent illustrative discussion of the use of handheld meters and both reflective (your camera and all cameras) and incident light meter readings.
As you progress, you might wish to obtain a good handheld meter and make use of the incident light metering method to insure more consistent results under all types of lighting situations.
5. Although Swedlund's book is excellent, there are two other still excellent books, which might be of interest.
The first is "The Eye of Eisenstaedt" by Alfred Eisenstaedt, who was one of the original photographers for Life magazine. This book is part autobiography, part photographic techniques, and part "seeing" photographically. One of the gems of this book is that Eisenstaedt shows you selections of his contact strips and then discusses why he choose a certain frame.
Again, this book can be found at or through your public library (inter-library loan system) or purchased at either of the two excellent sources of used books:
http://www.abe.com
or
http://www.alibris.com
Here are two links to this famous Life photographer.
At the first link, scroll down until you see the photos
"Premiere at La Scala, Milan," and
"Ice Skating Waiter, St. Moritz," and then read about them and then scroll down to read the final paragraph. Good avice!
With regard to the "ice skating waiter", you might refer to the discussion above regarding the anticipation of your subject at a point of arrival. The photo and commentary provide a good illustrative discussion of this point.
http://artscenecal.com/ArticlesFile/Archive/Articles1997/Articles0397/AEisenstaedt.html
The second site below will provide you with additional information. Take note of his "wise saying:"
"It's more important to click with people than to click the shutter."
The second highly recommended book is "Better Colour" by Walther Bensor. Although it is also a little outdated when referencing films and camera models, it is still one of the best books on "seeing" photographically. Again, you'll find copies at or through the sources previously mentioned.
There are, of course, other excellent books and photographers to explore, i.e. "The Woman's Eye" by Anne Tucker; "Halfway to Freedom" by Margaret Bourke-White - another one of the original photographers for Life magazine. The later book is an excellent example of both good writing and photography. It's a study of the forthcoming independence of India, etc. Margaret was the last western person to see and photograph Ghandi before he was assassinated. Margaret's biography is a good read as well.
6. One (almost) final thought - stick exclusively to Canon FD lenses!!!!!!!!!! If you can't afford to purchase a "new" lens immediately, save your money and then choose wisely. You'll be much happier and satisfied with your results in the long run.
Oh yes, always make use of a good (preferably - Canon) lens shade. If you wish to actually see what a lens shade will do, look through a toilet paper tube or a paper towel tube the next time you "sit" on the throne. Look at a shaded or a darker area - you'll see greatly improved contrast and clarity.
7. Now for one final thought. Although the site below might be a little technical, it's worth exploring and referencing (bookmarking) for future reference when and if needed.
http://www.imx.nl/photosite/technical/indextech.html
If you have need of any further information, please feel free to give us a jingle and we'll be more than happy to be of assistance.
My best wishes in your photographic explorations!
Bill
Good thing I have that 20D lying around somewhere 
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