So you're not familliar with those technical drawings, no problem:
N°1 is the imput shaft, on every gear except 4th power goes from N°1 to N°3 then to N°2 and to the diff.
N°5 is the pinion for 1st gear, N°7 for 2nd, N°8 for 3rd and for 4th gear the synchromesh N°9 links directly N°1 with N°2.
5th gear use pinions N°11 and N°12 and N°13 is for reverse.
Seeing those all day I tend to forget that it wasn't that easy to understand at first.
Here is another view:
I may have mixed BA10/5 and BA7/5 gearboxes on those drawings but that's not really important to understand the big picture.