Do you mean the forward and back commands bound to the green arrows buttons on the standard toolbar.
The navigate section of the help file says they're the same as next-buffer prev-buffer but that's incorrect.
The help file info for forward says
Go to the next viewed file and cursor location like a web browser. This function is only available after using the back command.
which does seem to be correct.
So if you start slick, then visit buffers a,b,c,d,e, the forward button is still greyed out (coz you haven't used back yet), use back once and you're at buffer d, use back again and you're at c,
then
forward -> d
forward -> e
back -> d
back -> c
back -> b
Now go to buffer z using file tabs toolbar.
back -> b
forward -> z
back -> b
back -> a
just like a web browser.
Graeme