3
In XOOPS parlance what you are asking about is called a "block". You can define a new block in "System" -> "Blocks" and then outline where it appears on a page (Left sidebar, Right Sidebar, or in the Center), and on which sections (modules) it appears. Once you have created a block, you will also need to give permissions to the appropriate groups to see your newly created block in "System" -> "Groups" under "Block Access Rights"