Slow down to speed up! Thats usually the single biggest problem with fatigue after a length or two.
Get proper lessons from a learn to swim teacher is always best. Dont get into bad habits.
If not, then learn to float first! Then start to pull yourself through the water. Rotate ~45degrees to get a better grip of the water with the larger muscles in the back for each stroke. Kicking helps balance, “6 beat kick” which is 3 kicks per arm pull.
Watch addlington videos and try and copy! GTN will have some videos maybe, and i like the bill sweetenham drill progression here.
You will be fine though, as long as you can float.