>>36322391First, do some land exercises; land exercises being regular pushups and a quick jog before swimming.
Following the land exercises, start off with 8×25 meter laps of freestyle non-stop. It's important to not stop on walls because we want your heart rate to get up to speed. You shouldn't go fast since you're not used to it, but also because it's just a warmup.
Because you want to work on treading water, learn to eggbeater in place. To eggbeater you want your legs, specifically your calves, to rotate towards you. You want to do this pretty fast since that's how you keep yourself afloat.
If you can't eggbeater in place for more than 10 seconds, just stop and take a break. Take deep strong breaths into your nose and out through your mouth. You want to keep doing this even while eggbeatering as you are not only training your upper body strength, but also your lungs.
Is there anything else you'd like to ask?