Check out the other posts for atlas first and foremost for the most depth and explanation, and please do ask the people who are better than me for advice regarding atlas (anything I say here should only be for beginners, like an intro guide for newbies if they still exist)
1st: a rundown of his skills
His basic: (it's the same as everyone)
His primary: shoots out a barrier which grows out depending on the amount of projectile range you currently have. (this is a projectile attack)
His Secondary: does a gojo domain expansion, temporarily creating a barrier while dealing high damage to targets (learning the range and adapting to it will be a very good idea if you look to be a main, which then refer to the other big boi atlas guide). (This is a creation)
His ultimate: a heal which doesn't have anything to benefit hitting the core away from him, although it might seem weak, positioning and timing of this thing is KEY. Rarely use his skill as a self heal or a heal in general (unless your teammates are staggered and playing on the edge) which leads me to the 2nd use which is when a fight is going on on the sides.
Alright done with that now. The fundamentals are key for atlas, as if you see, he doesn't have a SINGLE movement skill, which means he benefits from gaining a form of movement speed, additionally, its good to usually take strike shot as its the standard pick for atlas.
Things you can do within the OS server to develop basics.
JOIN CUSTOMS. Usually, there will be customs somewhere sometime within the server, where people will be playing on, playing with then can also teach you the basics of the game and you can develop with the people who are playing with you (and make new friends but aren't we all :D)
bc sleep