There are very few staff photographers anymore, Most are freelancers now. Some magazines will take submissions, some get so menay they just go into the trash.
It's about putting yourself out there and getting known. And a Lot of word of mouth. In some case now ,like Travel Magazines, the writer oif the article may be asked to provide some images. and they may either do them themselves or have a photographer they know shoot them and the writer submits it all.
It depends heavily on what type of magazine you are talking about because they can all be different from Paparazzi style photos for Pop culture magazine, to Travel, To Journalistic to Photography Magazine. and sometimes you never know where what will come from. I was known for shooting Jazz concerts and a magazine contacted me If I could get some images forthem I said sure what concert...they said...ummm None but you live in an area we need shots of some wineries. I said sure.
And the last photography Magazine I did, they had a new editor that was looking for new writers/photographers and she just asked around if anyone knew anyone and my name came up. But it's getting your stuff seen wherever you can, however you can and as much as you can.
Calendars depend, Some are of one particular artist. Others just have a general theme and the calendar company just go to Stock Image sites and finds the images they need...for cheap. Remembering that margins on calendars are TINY.
Put your images everywhere you can on the web. But you have to make sure you use image tags well or they will never come up in a search. If your image is tagged IMG_2456. You will never be found. Tga that Image. Rocky Mountain Lake Sunset. You MAY be seen by someone in a search.
But be prepared. Most peope that do find your images, even high end magazines will say " AND we will give you credit" which unfortunatley is not accepted at your supermarket. Always ask to be paid. But sometimes it is OK to do some gratis IF you think it will get your name in front of the right eyes. But be very careful with that and you would be surprised if you just ask for money what may happen. Someone saw an image of mine and wanted it for theer website banner and of course offered to "credit Me" I just replied back nicely I don't do that but you could buy it for this...never thinking he would go for it. He relpied back, sound great, I'll send you the money.
There is no easy answer to this anymore. Submit, Post your images, get a reputation, get your name dropped wherever you an...and ..TAKE GREAT PHOTOS