The totty is
very fine.
The easiest way to start is to commit to a short race. The standard short distance is 500-750m swim, 20k bike, 5k run. Pick a pool swim and you don't need any extra kit (always wise for the first one) otherwise you can hire wetsuits.
Here's British Triathlon's
event search. Things don't really get going until it's warm, so you have plenty of time!
Now, you'll need to practice your front crawl. The swim is freestyle, and people do events with breaststroke, but fc is the fast one. That means getting regular swim sessions in. Bike, well, 20k is a warmup for you - you ride it like a time trial, no drafting, aero and gurn it
Run - get some good shoes and pound the pavement with a long-steady run and a speed run each week.
The fourth thing to practice is transition: the changeover. Closer to the race, start doing combination workouts of swim-bike and bike-run (I set my running shoes ready when I get home from my commute, for example, or just ride to the pool and back). The swim-bike transition is pretty straightforward at this distance (at longer distances you get woozy as you've been lying down for so long!). The bike-run transition feels weird so it's good to do it a few times.
A cheerleader taking incriminating photos of you bending over putting your shoes on is always good. Stick all your stuff in a plastic crate next to your bike and lay out a distinctive towel too so you can spot your steed. Fixies aren't allowed, helmets are required - in novice events you'll see hybrids and full-sussers and shoppers, so don't worry about bling
For a pool event the start is usually done in waves, to stop pile-ups in the lanes (you post a predicted time before the event). In my first event, I was in the "barely able to swim at all" lane and we all kept stopping, breaking into breaststroke, gasping for air... it was a real clown show, but very good humoured.
Triathletes generally *are* very good humoured. I wouldn't still be doing it if everyone was sour and elite.
If you can run and swim to some degree of skill, then three months is plenty of time to get ready for a sprint.