I am gathering by your profile you work for Titan doing contract work for other airlines?
Firstly, I wouldn't buy a rating, it will inevitably be the wrong one.
Business or private jets range in size from Eclipses to A380s.
Freelance or part-time is difficult to get unless you know someone.
The job... Well. Depending on who you are working for it could range from you doing the flight planning and buying the catering to having departments to take care of that.
Even so, you still need to check and load the catering, clean and prepare the cabin, oversee the refueling, toilet service etc. You'll probably have to fetch the pax from the terminal or at least escort them to the aircraft.
You'll have to load the bags and most likely give the safety brief and settle them into the aircraft. If you don't have a FA, you'll often have to do a basic service, food, drink etc.
Tidy the cabin prior to arrival, check on the pax onward requirements (car etc).
Either hand them to the FBO or escort them through the terminal. Unload the aircraft, clean, tidy, refuel and either put the aircraft to bed or fly another sector.
Slightly more work than the usual airline flight.