Hi,
 
How can I display only main categories on the home page? Also, can I display subcategories when people go to the parent category page?
 
Thanks!
 
tw

Please go to Admin > CMS > Site Layout and look at the Layouts on the right hand side.
 
Click on the page you want to modify and select/deselect the blocks that make up each page to get the required layout. You can also change the order the blocks appear in.
 
If you need additional blocks you can create these in CMS > Custom Blocks and add these to any page.