Only Summary on front page

Use the “more” tag when you write an entry. I don’t think this button shows up in the rich editor though.

When you are writing an entry, there are buttons across the top of the text box.

What version of WP are you using?

See the list of QuickTags for an explanation of the <!--more--> tag.

The QuickTags documentation should still be valid, and it explains what the <!--more--> tag is, and why you’d use it.