Describing the Gmail method of organizing your kept emails as somehow like a folder is a little misleading. All your emails that you have not deleted are on the server as one entity. Click on the All Mail label on the left side of the Gmail window and you will see them all. If you look at all your emails in the All Mail folder, you will see what label(s) if any are associated with each email at the very left of its entry.
So when you click on a label on the left side of the window, Gmail simply displays those emails that have that label. When you are looking at the list of emails with a particular label, if it is tagged with any other labels they will show at the very first of that emails entry in the list.
No "folders" as exist in Windows are involved, but the same purpose is served.
The inbox by the way, is just another label.