The source linked debugger shows your place in your source code by positioning an arrow near the goal being executed or clause to be tried. The position of the arrow and the direction in which it points reflect which debugger port you are at (see dbg-bas-pbx).
To help you visualize how this works, we repeat the picture of the procedure box from dbg-bas-upe:
+---------+------------------------------+
Call | | | Exit
-------->| ------>| descendant(X, Y) :- |------->
| Head | offspring(X, Y). |
| | | Done
<--------| | |------->
Fail | ------>| descendant(X, Z) :- |
| Head | offspring(X, Y), |
<--------| | descendant(Y, Z). |<-------
Exception| | | Redo
+---------+------------------------------+