Photoshop help

Im trying to make jerseys in Photoshp CS2 9.0 using one of thw jersey tempalates and I dont know how to do a few things. When I make lines for trim I don't know how to cut boxes and lines so that you dont see them passed the armpit line. Kinda looks messy.
How do you guys get those elaborate trim lines?
Also how do you copy collars from the collars file to the jersey file?
I know there is a tutorial but even I cant understand it cuz the directions arent too clear.

For the armpit thing, I just take the Eraser Tool and get rid of the parts I don't want. Anything in the armpit hole (that's not on the rectangle) will not show up anyway, though.

Elaborate trim can be done many ways; you could use the Pen Tool to draw where you want the trim, then Stroke the vector line. I don't have the Pen Tool, so I have to make a selection and then Stroke that. Either way will work.

Copying collars is easy, just highlight the layer with the collar on it, press Ctrl+A (select all), then Copy it, go to your jersey, and Paste (it'll paste as a new layer).

Are the collar layers transparent?

I don't really know what you're asking, but the collar layers are only the collars, nothing else, so the rest of the space would be transparent, yes.