I hate to be the killjoy who says RTFM, but a question such as yours really does not require a specially formulated answer from fellow users in real time. Generally, questions regarding the program’s basic capabilities can be resolved rather quickly by looking them up in the documentation, which is variously referred to as the Help Center, the Knowledge Center, or the Knowledge Base. You can get there by going to the Help menu in SU and clicking Knowledge Center.
Out of curiosity I entered the exact same question into the Knowledge Center that you used to title your post here. Although the Knowledge Center can be a little hit-or-miss sometimes (in which case you should immediately come here for an answer), not so on this question. To my pleasant surprise, the KC came back with a thorough article explaining image file types and how to import them. Better and more complete, I daresay, than the off-the-cuff answers you received here.