The problem is that there are so many themes out there, all of which do ‘clever’ things with layout that it is impossible to give a set of instructions.
However you are using a paid theme with support, so you need to refer to them.
You question should look like
I’ve just installed bbpress forum software, and I want to use this in a page with a sidebar. To do this I need to copy and rename a theme page template that has a sidebar – basically I need to rename it bbpress.php and put it in my themes folder.
Can you either let me know which template file in your theme has a sidebar, or where within an existing template (having copied and renamed it) I would put something like
<?php get_sidebar(); ?>