My storage is being used up and I can't tell what by. Thanks in advance!
By looking at your screenshot it is clear that most of your storage is taken up by apps. Apps have a tendancy to store cached data. If you click on Apps and click individual apps by name you can clear the Cache files which can free up space.
Apps which have a large amount of cache data tends to be web browsers. An example of how much data web browser can store in cache can be seen below.
The cached data is your problem. Cached data is in a separate category that is hidden in general. You can clear your cached data by clicking on apps then selecting Google chrome, or something else, then clicking clear cached data. This will not effect your device. After you have done this for about 5 apps, go to the play store and download Norton Clean. This app will clean these caches and any other junk files for you in a millionth of the time.