OK, a Track Eraser is a tool that erases history tracks - list of websites you visit, cookies, list of your recently accessed documents and so on. It doesn't delete the actual files, just the listings. As for a File Shredder, you should use it only when you need to delete a file that contains your details (like an old bank statement). A File Shredder will delete the actual file in such a way that it will be impossible to recover. I've never used the one that's part of Glary Utilities, but I'm using Easy File Shredder on a regular basis.
Hope this helps.