I don't see what's confusing about the UEFA's rules. And World Cup group stage only plays each team once before moving on where CL gives each team 2 matches against each other. Reading the rules here, that's the only real difference and I guarantee a lot of people would be more upset with a 3 match group stage than a 6 match group stage where you can maybe get back at that team that took points from you before. Tie breakers are pretty simple, if you have equal amount of pts its goal difference. If you have equal goal difference its broken by who scored the most goals away from home. Usually it does not need to go down to such specific terms though.