It’s also a good idea to remove any debris or dirt that’s settled in creating ground contact with your joists.

You’ll need a level. You can brace the steel post to keep it straight or simply pound it in a bit to hold it. Then pour concrete in hole around it. Lots of videos online: https://www.youtube.com/watch?v=G6f98daPgFw If you’re using steel posts you can just bolt 2x4s to the steel. You don’t need 4x4s.

That appears to be a sono tube with a galvanized chainlink style post set into it. It’s easy enough to box around those with 2x4s to obtain a wood post look. You really don’t need the sono tube though. Nor would I leave it sticking up that far for just a fence.