It is important to adjust your bicycle for a perfect fit. This will increase pedaling efficiency, increase comfort, and help prevent overuse injuries. In my opinion, it is not necessary to pay for a professional bicycle fitting. Simply follow these step-by-step instructions.
The correct height for your seat is to adjust the seat post so the HEEL of your bike shoe just barely loses contact with the pedal at the lowest point of the pedal stroke.
Your seat also adjusts forward and aft. Have someone help you with this adjustment. It is correct when your foot is at the point of maximum power (knee bent 90 degrees) and the center of the knee (center of rotation) is directly over the center of the pedal spindle (center of rotation). A plumb bob would be perpendicular between these two points.
Your saddle should be very close to level. It is generally permissible to have the nose of your saddle very slightly up or down based on what you find most comfortable. Too far down, however, can cause you to slide forward and puts more weight on your hands. Too far up, and the opposite can occur. Perfectly level is usually best.
Your handlebar height is adjustable by moving the stem up or down. This adjustment is primarily for comfort. Higher helps your lower back and puts less weight on your hands, but it does put more weight on your butt. I prefer a higher adjustment because sore hands are a big issue for me. (Some modern bicycles lack this adjustment or can only be adjusted using spacers.)
You can also tilt the handlebars. I like mine tilted so that an imaginary line running parallel to the lowest dropped portion of the handlebar and extended towards the rear of the bicycle runs through the center of the rear hub. This tilt makes the brake hoods comfortable to grip when I’m climbing off saddle.
Finally, the cleats on your bicycle shoes are another critical adjustment. I carefully adjust mine so each shoe is as far as possible to the outside of the bicycle. This prevents heel rub on the crank arms. Next, move the cleats fore or aft so that the center of the ball of your foot exactly aligns with the center of the pedal spindle. This is the only point where your foot bends. Align any other part of your foot with the center of the pedal spindle and you risk severe foot pain over time. I learned this the hard way.
Riding a properly sized and fitted road bike is a transformative experience. It feels efficient and it feels incredibly comfortable!