>> 1/2 bath to 3/4 bath home improvement

I own a 54 year old house and I want to convert my
1/2 bath to a 3/4 bath by adding an upright shower. The room is "L" shaped
with a toilet at one end of the "L" and a sink at the other. The idea is to
make the room square by demo'ing the closet that makes the room "L" shaped.
I have very little experience but a lot of guts. I have a professional who
will hang the drywall after I am done installing the shower. My biggest concern
is tapping into the existing plumbing. My plumbing questions are: What supplies
will I need? How difficult is this project? How do I do it?
Thank you,