To add a divider that will split your portfolio into sections, ensure that you are logged in to your account. Mouse over the 'Add Item' button and then click 'Add Divider'.
You can rearrange your work under each divider by clicking 'Move Clippings'.
Dividers automatically appear as filters for logged out users. You can see how this will look when you're logged in by clicking 'Preview' on the top bar.