1st and best advice is to understand your initial setup
... a 3 axis vertical machine, the part face is placed in the TOP plane, so the FRONT, BOTTOM planes fall correctly. You may have to create a new BACK plane, as it may be up-side-down( depends on post).
... a horizontal is different, the TOP WCS is the view you see looking from the Y+ position. The B0 face is the FRONT face. So B90 makes the RIGHT face, B180 is BACK, B-90(B270) is LEFT face.
If you use a different co-ord system for each face, there are methods to assign a system to each view
If you are programming only the TOP face, you can have the part face set as TOP WCS
Each toolpath requires "planes" to be set before selecting cut parameters
NOTE... make sure that tool has retracted BEFORE any index (B) moves... spindle crashes on a horizontal can be expensive.
Take little steps, it takes time
Remember... WCS is always TOP, C & T plane is what you want the tool to address.