How does goal difference work in Champions League?

Related questions

1. How much does the World Cup winner get?
2. How do you calculate goal difference?
3. Does FA Cup winner qualify for Europa League?
4. Who score the fastest goal in 2018 World Cup?
5. How are premiership points calculated?
6. Who has won the most league titles in the world?
7. What happens if points and goal difference are the same?
8. Who is the richest club?
9. How many teams have won the EPL?

Tags

1. #points
2. #still
3. #decided
4. #third
5. #league
6. #difference
7. #result
8. #champions
9. #goals
10. #followed
11. #example
12. #since
13. #group
14. #shootout
15. #penalty
16. #stage
17. #legged
18. #tiebreaker