SQL Server / SSMS taking up lots of disk space

I installed SQL Server + SSMS for my univ class and ever since then my disk space is going missing (every so often, approx. 3 gb of space goes missing). I strongly suspect SQL Server and/or SSMS to be at fault (since it only happened after I installed them), however I have no idea how to track down that missing space. Is it doing massive amounts of logging? Backups? No idea.