On my mac, there are Library folders and System folders that have lots of weird folders, would I ever need to touch them? Also do they take up lots of space?
If you don't k now what is inside, look into them, BUT DON'T DELETE ANYTHING you don't know something about.
To get the size of a file or a folder, select it and press CMD+I.
Btw, the folder called "System" is important for the operating system (OS) Mac OS X. The "Library" folder is also important.
If you want to delete something, best do it inside your Home Directory (Macintosh HD / Users / YOU), while you have already a backup account created to log into in case you deleted something important.