Hi Hank
I'm a newbie with Realband and BIAB and have been playing around with the BLOCK menu a bit.

As I see it the purpose of the BLOCK Menu is to select certain sections of the track you are on so that you can either Cut or Paste or Generate a Realtrack in that part of the track.
First you need to look at the green numbers in the Now, From and Thru boxes at the top right of the RB window.

If you don't see these windows you may have to stretch the main RB window out or click on the little black arrow
at the far right to make it show these windows.

The green Now numbers change depending on where you place your cursor and click or where the song on that track is playing.

The From and Thru numbers indicate where you started and stopped if you hold down the mouse button and select a portion of the track, that you are on, to edit.

If you need to be very exact you can enter the green From and Thru values of the part you want to select using From=Value or Thru=Value commands.

The Select Current Selection makes selection according to Markers you have inserted in the song to designate things like Intros, Chorus's or any other reason.
Note as a newbie I have not experimented with the Markers Window so can't advise on that.

Choose Recent Selections lets you select the same green time zones as you go down through each track.

My suggestion is to try selecting a section or Block then Copy it (Control+C), then select another block and Paste it in and see how it works.

Hope this helps you a bit.
Just play around with it and you'll either get the hang of it or maybe a veteran can explain it better than I.
They have helped me a lot.

Good luck and keep on makin notes.
Carl