2
You need to select a 'module' as your start page and make sure the 'welcome' block is set to center with a ranking of 1. All else will come below this. A lot of this is explained in XOOPS docs in the link 'find help docs here' below.
Go to admin, general preferences and set a content block like news as your start module.
Go to Blocks and set those blocks you want to have appear on right, center, left and their ranking by number.
All of this applies if you are using 2.0.13 versions - not sure about 2.2 version of xoops.