First, highlight the section you would like to clip.
This is a little tricky: select (i.e. click and drag) the part of the page you would like to clip BEFORE doing anything else -
just as you would cut-copy-and-paste text on a regular app.
Then, click on the Clipclip button.
After you have selected the part you would like to clip, click on the Clipclip button on the toolbar.