Hi Leili, we used to have that, and I don't think you can actually do that any more, well I haven't done it since about after transitioning to v2.1 I think. The reason was that this structure was common to all Moodles until about v2.1 (from memory) but the issue it caused was named "The Scroll Of Death". All it did was to create a very long list of courses that would take forever to scroll down if your course was recently created and very east to miss amongst the gamut of courses listed. Moodle now allows you to set the first page as the Dashboard of the User
, and in that you can, I understand, lay it out as you like. I don't use that as both my front pages are set out in a table form, have been like that forever, with each subject given its own place, its own images and rollovers. I did try to change it once, but got so many complaints about how people were unable to find things I had to go back. Good luck.