Set the saddle height correctly. Wear whatever shoes you will wear cycling, stand the bike by a wall, get on it, use the wall to support yourself, put your heels on the pedals, and pedal backwards, keeping your hips level. When the pedal is as far as it can be from the saddle, your leg should be straight and your heel barely touching the pedal. Adjust seatpost as necessary.

Adjust saddle tilt. Make the saddle level, meaning a large book or ruler placed over the nose and tail of the saddle is horizontal.

Adjust saddle position. Adjust the saddle in the seatpost clamp so that the seatpost is roughly at the center of the saddle.

Set handlebar height. Since you are just starting with a drop bar road bike, adjust stem so that the top of your handlebar is roughly the same lever as the top surface of your saddle. That is a neutral sort of position where most people are comfortable.

Wear cycling shorts, or at least tight underwear that holds your private parts. This is not a time for boxer shorts.

See how that works.