How do I change how my pages show up in Google (the title and description)?

In Settings → Search and redirects, each page has its Title in Google and Description, which you can edit.

They start out Automatic, written from the page's words and what you're known for. Once you edit one, it's marked Edited by you and kept as you wrote it. Reset to automatic brings back the written-for-you version. Titles can be up to 70 characters and descriptions up to 170, though Google often cuts titles near 60.

On a live site, your changes save to your draft: publish changes on the Site tab to make them live. Google updates its results on its own schedule, so it can take a while to show.