How would I connect another building to our network?

I have two switches in two separate buildings. One switch has FTTP and the other has no wan connection. I was looking into running ethernet between the switches. The building is only around 50m away.

I was looking into using SFPs with an RJ45 connection, what is the benefit of this?

Why couldnt I just run ethernet from the 1st switch to the 2nd and just plug it into one of the ports not needing to use SFPs?

How would you do it?

Thanks.