This study explains the rules of atomic chess in detail: https://lichess.org/study/uf9GpQyI
In Atomic the kings can be connected by moving one into the adjacent squares of the other side’s king. When the kings are connected, checks do not apply. As it is illegal for a capture to blow up your own king, it is not possible to capture the other king directly. To win such an endgame, it is necessary to cause the kings to detach by zugzwang or explode a piece of the opposite color while the king is next to it.
Interested in learning more about atomic chess? Here are some resources to help you!
Openings
Opening Queen Tactics https://lichess.org/study/sRM1FScZ
Opening Knight Tactics https://lichess.org/study/12TFMoys
Introduction to 1.Nh3 https://lichess.org/study/Toy8tRrm
Introduction to 1.Nf3 https://lichess.org/study/M6TaslQW
Endgames
Basic Endgames https://lichess.org/study/ikJM4K3L
Intermediate Endgames https://lichess.org/study/tCqrXrbG
Advanced Endgames https://lichess.org/study/WOWizkm4
Endgame Practice https://lichess.org/study/wRLQk6Wq
Other
Atomic Chess puzzles https://chessvariants.training/Puzzle/Atomic
Atomic Chess video series made by the 2016 Atomic Chess World Champion https://www.youtube.com/user/tipau
Excellent advanced Atomic Chess resources https://illion-atomic.netlify.app/resources/
You can join the Lichess Atomic team for more content and community-driven events!