google is your friend here.

Also heartless makes a great point. If you have access to solid works why are you seeking random downloads of stls.

The difference in having a 3d printer as a toy versus a tool is the ability to create files. 

also keep in mind may files have some sort of copyright  or restriction.
Usually  one can downloads and modify for personal use but not commercial/ monetary gain.

Another thing stl files are not necessarily the best to modify, customize or otherwise work with.

This is because the stl format often lacks details contained in the original design format.

Also if you are doing this to make homework easier this could be considered cheating. Depending on the assignment criteria.
If your goal is to learn solid works there are plenty of tutorials on you tube you can reference.

if you have access to solidworks, learn how to use it and start creating!