You can always add content to XOOPS by adding a "custom block". That's the easiest way to add text or html and position it on your site.
The Content modules allow more versatility for custom pages, text, etc...so that you can call up specific content by a web address, for instance. On the A is for Antiques website, I used a module called Multimenu to allow me to link to pages in the Content Module. When you click the "about us" link, it takes you to the custom content I added to the content module.
Blocks - you can add a custom block and have it appear on any page in any of five locations. On my site, I have an "About us" link in the main menu. That link takes the visitor to the content I added in the Content module (Content version .5), as mentioned above. In addition to the "About us" content, all sorts of different blocks are visible on that page as well.
The Main Menu is a block (from the Multimenu module), the random images under the Main Menu is a block (from the XoopsGallery module), there's a scrolling marquee (Marquee module) and a couple of other custom blocks in the right column. And in the center block of the main page is a custom block with the big picture, underneath it is the "recent news" block that comes from the News module, etc...
Each module will have a number of blocks that can be used with it - the News module has a recent news block, a news by topics block, etc. You can use all of them or one, or none of the blocks, and you can position them wherever you wish.
If you'd like specifics as to exactly what modules I used on that site, let me know.
Not all modules are compatible with the current version of XOOPS, since it's so new. Looking and searching through the forums for compatibility is the best way to get information as to which modules work (...asking questions helps, too).
Take care...
JC