How to know what model of Digital SLR camera to buy?

I'm going to get a Digital SLR camera for my birthday, but there are so many different models! I want a Nikon, and it has to have recording and picture options, good quality, manual focusing, ect. Basically the main functions of SLR cameras. I don't want it to be too expensive, but also not so inexpensive that there's poor quality or not enough features. I take some photography and I would like to use it for that.

Depending on your level of comfort NIKON has several choices that do both photo and video capture. If you are newer to dslr then a good option might be the NIKON d3100. Does 1080p video with a nice sensor for image capture. While it affords the ahooter with manual capabilities its also equipped with preset modes that you might find helpful.
I personally have the NIKON d300 and bought a NIKON d7000 for my girlfriend. NIKON has an excellent range of glass to select from. Odds are however if you get the kit lens it will do everything you need. As your skills improve you can opt to upgrade glass for better quality images based on composition.

I would suggest the D3100.It runs for about $650.