MIG (GMAW): Argon, Ar75 or CO2 depending on metal
workpiece and penetration desired. Straight argon for
aluminum.
TIG (GTAW): Argon, helium
Stick / flux cored wire: none
Gas welding: Acetylene generally, but heating and
low melting point materials may prefer oxy/propane for
cost (aluminum, brazing).
I question just how good a shop it is if the owner has
no clue about the processes used. Certainly seems
likely to foster a lack of respect from the people doing
the actual work. Go take a welding night class at the
local community college, if you have one. Reading is
all well and fine but technique lies with "muscle memory",
more than book learning. Take it from a guy who's laid
down tens of feet of crappy welds.