Hello, thank you for taking the time to post your question!
You just want to be sure that all possible outcomes are accounted for … you have 2 possibilities at each flip so you end up with a total of 2 x 2 x 2 = 8 possible outcomes. I would break it down systematically then based on which one is picked first.
The ones that begin with Heads:
HHH
HHT
HTH
HTT
The ones that begin with Tails:
TTT
TTH
THT
THH
I hope that helps get you moving in the right direction! Feel free to reach out if you have any additional questions beyond that :)