I'm looking at the "Sometimes you have to take a step back to move forward".....

P(A∪B) Formula

The symbol "∪" (union) means "or". i.e., P(A∪B) is the probability of happening of the event A or B. To find, P(A∪B), we have to count the sample points that are present in both A and B. So is P(A∪B) = P(A) + P(B)?

No, because while counting the sample points from A and B, the sample points that are in A∩B are counted twice. Thus, we need to subtract P(A∩B) from the above sum to get P(A∪B).