Merging faces across from each other

Artwork Works in Progress
1

I am trying to figure out how to make these support beams for the roof of a well from a Grant Abbitt tutorial I am working on, but I don’t know what to do. Any help?

2021-04-10 (1)
2021-04-10 (1)1366×768 184 KB

2

afbeelding
afbeelding546×693 58.8 KB

This option in your context menu (also known as 'Bridge Edge Loops) will do the trick, if I understand your question right.