In what case do players attack each other?

mmm are you sure you read a bit before joining eve? google “eve concord” will bring you there CONCORD - EVE University Wiki
where the very first sentences say " It’s important to realize that CONCORD isn’t there to defend you, they are simply there to enforce the consequences of breaking the law. As such, people are able to break the law at any time of their choosing, as long as they are ok with the consequences.

This distinction is paramount to understanding how EVE works and why suicide ganking is valid game mechanics. The loot and consequence mechanics help serve as a self-regulatory risk vs reward system,"

once again, you should really join a corp