Open the Folders Module. To add items to a folder, check the box next to one or more rows in the table, then click 'Group Actions > Organize'. You may organize the table by module, if needed.
A window opens where you can search for and select the folder (or folders) you want to add them to, then confirm. You can add items to more than one folder at the same time — you don't have to repeat this step for each folder.
Removing Items from a Folder
To take an item out of a folder, open that folder, select the item, and click 'Group Actions > Remove from Folder'. This only removes the item from that one folder — it doesn't delete the item itself. If the item is also in other folders, it stays there. If that was its only folder, it goes back to Unorganized Items.