conduit in unfinished area?
Nonetheless, almost all Codes requires you to cover sheathed electrical cable with some sort of fire-rated wallboard (typically plaster of drywall) in order to run it between studs. Otherwise, you must use conduit to protect your wiring. (Note: do not put sheathed electrical cable inside conduit; it will overheat and is a code violation everywhere). There are also exceptions for attics or elevated ceilings, but the nuances vary too much to answer here.
You generally do not need to install a seperate breaker in a detached garage. I would check with your local electrical inspector. They will answer questions like that for you.