Well, they might not be called "folders", but Gmail's labels act a lot like folders do. Using filters, you can even have Gmail sort your incoming mail by sender, subject or other criteria to your custom folders — out of the Inbox.
Use Gmail as if It Had Folders and Filters
To make Gmail route certain mail to particular "folders", bypassing your Inbox:
- Click Create a filter.
- Enter the desired criteria.
- To filter all mail from somebody, type their email address in the From: field, for example.
- Click Next Step ».
- Make sure Skip the Inbox is checked.
- Also check Apply the label:.
- Select an existing label (folder) from the Choose label... menu or:
- Select New label....
- Type the desired name for the label (folder).
- Click OK.
- Optionally, check Also apply filter to conversations below to move existing messages matching your criteria to the folder.
- Click Create Filter.
New messages matching your rules will arrive in their labels (i.e. folders) only. If you keep the Labels box on it and an eye on it, you'll see labels with new messages highlighted.