How do you draw a tree diagram to determine the number of outcomes?

Well you start with the first event, how many possibilities, draw a line down for each one, and state what event occurred. I.e. a heads or tails of a coin.

Then from each of these outcomes, draw the possible outcomes from each of the first events reflecting the second events, i.e. HH, HT, TH, TT. Third outcome (third flip of a coin) would look like this. HHH, HHT, HTH, HTT, THH, THT, TTH, TTT