How can i add?

Hey.

How users can add images to their images / files folders?..

That their folder would have own image :P 

Are you asking how to upload photos, or how to add photos as an icon for albums?

You can upload photos from Photos -> My albums -> P's photos (where P is the name of the profile (and the default album)).  There should be a Main block with a link to upload new photos to the album.

For adding an icon to albums, this is already done.  The album will display up to four photos from the album.  If you need something more custom than that, there's a jobs area: http://www.boonex.com/jobs