If I rename a page, do the links to it break?

No. When you link a word to one of your own pages, pick the page from the list rather than typing an address. The link remembers the page itself, so renaming that page later moves every link with it.

To make one, select the words and choose Link. To change or remove one you already made, right-click it: the menu shows where it currently goes, and offers changing it, removing the link while keeping the words, or opening it in a new tab. Links to other people's sites open in a new tab on their own, so you never have to think about it.