Best way to do it is to start breaking everything out on a spreadsheet in excel with him sitting there:
Start with income, then start taking things away from that money. Work on a monthly basis, because people can understand payments on a monthly basis.

Income = _____________
FICA
State Income Tax
Medical Insurance
Dental Insurance
Take Home = _____________/yr then __________/month (This is where you start)

-------- (start subtracting)
Food _____/month
Dinner out = 50$
Truck/Car = ______month payment + $0.55 per mile you plan to drive
Rent/Mortgage
electric
gas
water
cell phone
TV
computer
internet
cable TV
go to football game/movie/night out
medications
clothing
hunting
fishing
boat
boots
furniture
travel
401k/savings
gonna have a hospital stay at some point

Baby..... (20 doc visits by mom / vitamins, etc)
Daycare = $125/month until 2yrs old
car seat
meds
food
etc

teenager.....
car
college
another phone