Wow. Some of those questions are super basic and it would be a crime for you to waste money on it.
1: Recording pictures on a memory card - Your camera will handle this. Theres really nothing you need to know about how they do it. Now, if you're talking about "how well" they do it, that all depends on the media involved. Currently there really are only "two" media formats you'll find on a digital body - SD/SDHC and Compact Flash. What you will be looking for on the D90 is SD or SDHC. Kingston, Transcend and Pny make cheap (cheap does not mean CRAP) cards. Sandisk and Lexar are generally more expensive, and thus "better built" - although all of that is subjective. From my personal use, unless you have a NEED to fire shot after shot after shot, Kingston and Transcends 133x line and Sandisks Extreme III line of cards will suffice. You can google memory card timings for more information about this.
2. Transfering from computer - Most manufacturers will include software with your camera body. On a Nikon D90, it really is as simple as putting your camera in "Media Storage Mode" and drag and dropping your files to your hard drive. I personally use Adobe BRIDGE to capture the files, and then work on them in Photoshop or Capture NX. The "speed" at which you download files depends on both your Memory Cards read speed, and whether or not your computer has the capability to "read" them as fast. More often than not your computer will be a bottleneck, but it rarely takes me more than 10 minutes (that is a SUPER liberal estimate) to download about 4 gigs worth of pictures.
3. Printing - Wow. Well, you need a printer. Depending on what kind of prints you want to make will determine what kind of printer you go for. Is the most you want an 8.5x11 for framing? There are several low cost printers to do this. I use an HP D7360, but its no doubt discountinued by now. Thats a good consumner photo printer. If you want to do large prints the Canon Pixma 9000 is well rated, as if the Epson 1400 and 1800. Farther up the pay scale are the Canon Pixma 9500 and the Epson 2400. Another consideration is whether you want to go with "pigment" or "dye" based ink system. A google search can shed further details on that.
4. Learning Photoshop - Hooboy. Best to hit up Amazon or maybe Photo.net for some recommendations there. [ame=http://www.amazon.com/Real-World-Adobe-Photoshop-CS2/dp/0321334116]Real World Adobe Photoshop[/ame] might be a good place to start although it IS hefty.