If you want to use one of my files, you can choose whether to do that under the conditions of cc-by-sa-3.0 or cc-by-nc-3.0]. This applies to all files where I am the uploader as well as the author. Files that were created by somebody else and only uploaded by me are only licensed under cc-by-sa-3.0 (unless otherwise stated).
cc-by-sa-3.0 allows you to use my files even for commercial purposes, as long as the author (me) is attributed, and any derivative works are shared under the same conditions as well.
cc-by-nc-3.0 allows you to publish derivative works under any license you choose, as long as you make sure the author (me) is always attributed and the work is not used commercially.