When your typing the content into the editor in Silverstripe, type all the headings, and then all the content down the page. When you are finished, highlight either part of the content (the first word or sentence) or else a heading right above it, and then click on the anchor button in the editor. Give it a name for what you want the anchor to be called. Then go back up to the top of the page where you typed out the list of the of the contents. Highlight one of the headings and click the link button in the editor, choose the Anchor on this page option, and then type in the name of the anchor you previously gave it. Choose whether you want it to open a new window or not, and then click insert link.

Hope that helps, sorry if its a little messy on the explanation. Had too many thoughts in my head to concentrate properly.