Hey, welcome!
There are three things to consider when buying an SD card.
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speed (class 4, class 10, extreme, extreme pro, UHS..) Speed is important because slow speed means you need to wait longer between photos. It can also cause problems with videos. And loading photos to your computer takes longer. So you want a card that is as fast as the camera. But its pointless to buy a card that is much faster than the camera.
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size (8GB, 16GB, etc.): I would suggest you buy two smaller cards rather than one big card. 32GB is a lot of space, you probably won't need it unless you are going to take lots of video or travel for a long time without being able to save photos to a computer. The reason why its better to have smaller cards is because if you lose one or it gets damaged, you don't lose as much. Also, smaller cards aren't as expensive. I think 8 to 16GB should be more than enough for still photography, even if you take raw photos (jpegs are even smaller). 16GB and above is mostly for large videos
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brand. Brands of the card are pretty important. Sandisk is probably the best choice, they have a good reputation and make high quality cards. We haven't had many reports about problems with Sandisk. I would advise you avoid Sony.
There are also different types of SD cards - SD HC, SD XC,... this shouldn't matter as long as your camera has the latest firmware update. If you don't know what that is, there is a tutorial on this forum as well as a video and numerous threads about it, just search for it