Your camera supports SDXC cards which have a theoretical size limit of 2 TB, so it supports any SD, SDHC or SDXC memory cards on the market.
The difference between SD, SDHC and SDXC is maximum capacity. SD cards are limited to 2 GB. If you shoot video, you will notice that limit quickly. For images, it depends on how much you shoot and how often you offload. SDHC cards go up to 32 GB which gives space for thousands of photos. Your camera manual has a table near the end to let you know how much photos and video fits in different sizes.
Pick a size you are comfortable with. Some people decide to have one huge card and never swap and others like smaller chunks so that if one fails, you still have other cards and you lose less. Even top-notch cards can fail, so I strongly recommend more than one.
The card rating is prominent on most packages except for the slowest cards :) If you need a class 10 then you need one which says 'Class 10' or at least 10 MB/s or at least 66X. Some manufacturers use different measuring systems. Today you can get cards up to 1000X or 95 MB/s which is faster than your camera can take advantage of.