I want to try out for swim team in high school but i dont really know how i should train and what 2 train 4?

i am in 6th grade currently but i want to start training to get into swim team in high school. i dont really know quite how to swim for this and what kind of swiming i have to do. i have a large above ground pool in my backyard that iis about 3 and a half foot deep./ i am not very good at diving, so if u can give me some advice on that that would be great to. i cant practice in my pool how 2 dive, its 2 shallow but my friend has a diving board that i can practice diving on. but i find it really hard to dive without a diving board. so give me advice if u are on a swim team and PLEASE help me out :)