linking from thumbnail

I know this has to be easy but I am not well versed in web design and am helping a friend out.

On the site I’m working on

I would like to make the three thumbnails from the main page (“About us”, “Upcoming Events” and “Join Us” link to a different page.

I can only get them to link to the page I made the post on with the featured thumbnail.

I read how to add custom links on page but didnt seem to have any luck.

Can someone please let me know step by step how do to this?

Please let me know if I was not clear enough.