Collision and / or Mouse Camera Position

I am working on a game where I require two things, physics collision events and mouse screen position raycasts. I attempted to switch to the new DOTS Physics system however due to the screen raycasts not being in the new system I could not get the old system converted over to a DOTS Physics compliant method. However, I am struggling to get old physics working for collision events as I barely understand events to start with and converting to something ecs compliant is proving difficult. a solution to either of these problems would be a great help and both would surely give me a cavalcade of information to learn from.

Edit: I understand normal collision events however I don't know how I would go about changing them to work well with ECS so I can call them from a system.