Creating a trigger, function and a procedure in SQL

Hi,

I have 3 tables namely,

1) Vehicle (vehid, vehno, type, seats, status)
2) Driver (drid, dname, phno, address, status)
3) Hiring (hid, hdate, vehid, drid)

How can i create a trigger that checks the status of vehicle and driver for hiring
How to create a function that returns the number of vehicles that are available for hiring and
How to create a procedure which prints the hiring information with corresponding vehicle and driver information.