If you flip a coin twice what is the set of possible outcomes for this?

Let H mean Head and T mean Tail.

The outcomes from flipping a coin twice are the same as flipping two coins together. You might get H + H, or H + T, or T + H, or T + T. So there are four possible outcomes.

They are each equally likely but if you ask, "What are the chances of throwing H + H" the answer is 1 out of 4 or 25% or 0.25, and the same for throwing T + T.

However, if you ask the question, "What is the chance of throwing a H with a T the probability is 2 out of 4 because there are two ways of doing that. So the probability there is 2 out of 4, or 1 out of 2, or 50% or 0.5