You'll have to either be dropped off at the curb by private car, taxi, limo or commercial shuttle vehicle and then walk through the doors into the terminal. You could also park first and go to the terminal from the parking lot/garage.

Once you enter inside then proceed to a check-in counter. The line can be labeled domestic first class (but you can also you the economy check-in area). You can wait in line for an agent or use the check-in terminals (called Easy Checkin). If there is no line then just head directly to the counter/machine.

Note you can already be checked in. However if that is unclear then just present yourself and your baggage to the counter. T

The agent will tag your bag, hand you a claim ticket and then put it on the luggage belt.

Good Luck!