What do i need to do to fly at 16yo?

If you are under 18 and flying domestically (within the US), you do NOT need any ID.

Since you are flying Southwest, they do not offer Unaccompanied Minor service at your age. You are able to go through the process of security and getting to your gate on your own. But Southwest is very generous in issuing gate passes to allow an adult to accompany a minor to the gate; you can ask at the airline counter when you arrive.

YOU NEED an ADULT at Check in. They do not need to hold your hand after that.
As part of check n process ID needs to be shown. That is what the Parent is for.

An adult to check you in, you do not need ID and usually the airlines will issue the adult with you a pass to go through security and wait with you.

At your age you are considered an adult flyer. If you have no ID, you need a parent to check you in. If you have government or school issued picture ID then parents do not need to check you in.

My daughter flew back and forth between LA and Vancouver several times from age 14 to go visit my ex. She never got unaccompanied minor service.

all you need is for your parents to pay the extra fee for an unaccompanied minor and you also have to make sure someone of legal age is receiving you at your destination.