One thing that it vital that you know about your camera is what “crop” sensor it has, if any. So, haul out your camera manual and look at the specifications pages. Or do what I just did and Google it.
Please read the following article by David Rowse at Digital Photography School (an excellent resource, by the way): for an easy to understand explanation Crop Factor Explained.
The important thing to remember is to keep this number in mind when purchasing and selecting lenses. One of my cameras has a 1.5 crop sensor, so I must bear that in mind…when I choose my 85mm 1.8 lens for a studio shoot, I must remember that the crop factor will make the lens appear to be 147mm (1.5 crop times 85mm) – see how that works?
When I bought my fisheye (10.5 mm) I needed to bear in mind that the distortion I was wanting was only going to appear to be a `15mm lens instead.
Here is a pretty neat video Full Frame vs Crop Sensor Comparison that shows the difference between the 1.6 crop factor of a Canon 7D and a full-frame Canon 5D.
You should review these two informational sources and your camera manual until you know what your camera specs are and have a reasonable idea of how that affects your lenses. This informational will be relevant whenever you are purchasing a new lens, so get familiar with it so that you aren’t disappointed with future purchases.
I’m sure the question on the tip of your tongues is “which is better?” – here is another article by Darren Rowse that discusses this issue Full frame Sensor vs Crop Sensor – Which is Right for Me?
See? that was easy! Read a couple of articles, view a short video and boom, you have armed yourself with some useful technical knowledge about your gear. High Wootness Five!