It indexes classes and methods (symbols)in your project folders based on the syntax definition of the language in the file. You can then look up and search all symbols in your project, or Go to a symbol where your cursor is. It isn't "smart", so it doesn't know where you use which symbol, or which symbol is assigned to a variable. I haven't used it for mixed projects yet, so I can't say how it works there.

When you press Ctrl+Shift+R (Windows), it opens a panel similar to Goto Anything. You can then type the function, class or whatever and it will bring you right to it.

Also, when your cursor is on a word, and you press F12, it will bring you to the definition of the class or function. This also works with CSS classes and ID's from your HTML.