The Layouts page of the Site Admin allows you to control which side blocks are shown on the different pages of your site, and for the home page which middle blocks are shown.

Adding Layouts
By default your site has one layout which is used for all of the pages on your site. If you want a more advanced setup you can create more layouts by clicking the "Add Layout" button. When you create a new layout, you get a blank layout with no blocks, that will not be in use.

To use your new layout, click on the "Applied to 0 sections and 0 pages" links at the top to assign your layout.

For example, say you want the majority of your site to be 3 columns with blocks shown on the left and right, but you want your Forums and Events pages to be 1 column so they have more room to show their content. You can create a new layout called "Full Page" and then apply it to the Forums and Events sections.

Adding Blocks
To add blocks to your layout, click on the "+" button at the top of the column you want to add a block to. You will then be shown a popup allowing you to choose which block to add, and set any additional options on that block.

Note that most blocks can also be edited on your guild site, by clicking the edit icon at the bottom of them.