Learning to swim as an adult is a different experience from learning as a child, and almost every guide is written for children. This one is not.
The list
A proper swimming costume. For men, trunks or jammers rather than loose shorts — shorts create drag, and most pools will not allow them. For women, a one-piece is easier to forget about while you concentrate on something harder.
Goggles. Not optional. Being unable to see underwater is most of what makes early swimming frightening, and goggles remove that in one step. Test the seal by pressing them to your face without the strap — they should hold for a second on suction alone.
A towel. Obvious, and forgotten weekly.
Flip-flops. Wet poolside tile is the most slippery surface most people ever walk on.
A cap if you have long hair. Many pools require one regardless.
The two things adults forget
Water to drink. You sweat while swimming and cannot tell, because you are already wet. Adults regularly finish a first lesson mildly dehydrated and put the tiredness down to fitness.
Something to eat afterwards. Swimming makes you hungrier than it feels like it should, because your body is spending energy staying warm as well as moving.
What not to bring
A nose clip, at least not yet. Breathing out through your nose underwater is the foundation of everything that follows, and a clip stops you learning it.
Your own floats. The venue has them, and knowing which one to use when is part of what a coach is for.
What a first lesson actually involves
Almost certainly not swimming.
A good first session for an adult is spent getting comfortable putting your face in the water and breathing out slowly. Every stroke rests on being relaxed while submerged, and nothing can be built until that is there.
Expect to stand up often. Expect the shallow end. Expect it to feel slower than you hoped.
Adults learn more slowly than children for one reason, and it is not physical: adults have learned to be afraid of water and children mostly have not. The unlearning is the work, and it is real work.
How often to come
Twice a week beats once a week by much more than double. Water comfort fades between sessions, and a seven-day gap means spending the first fifteen minutes recovering ground you already had.
Twice a week for six weeks gets most adults swimming a length. That is a realistic target, and a modest one — do not let anybody sell you a faster one.
One last thing
Tell your coach you are nervous, if you are. Every swimming coach has taught frightened adults and none of them thinks less of you for it. The only thing they cannot help with is something they have not been told.
Swimming at KGB is on the same flat rate as every other sport, and coached sessions run for all levels including complete beginners.