What does getting a tune up mean, and how often should it be done? Does it have anything to do with how many miles you drive a year?

Depending on the vehicle, it can mean many things. On your 1993 Accord, I would say it would include changing the spark plugs (NGK only), distributor rotor, distributor cap, and possibly spark plug wires.

Spark plugs should be changed every 24,000 miles or 3 years, whichever comes first. This is for "copper core" plugs. Rotor, cap, and wires should be changed every 60,000 miles.