how we know the possible outcomes of tossing 3 coins i didnt understand hhh ttt etcc plzz fast

Each coin has two possibilities head (H) and tail (T).

So when you toss 3 coins you may get H on first one, T on second one, H on third one which is indicated by HTH.

Similarly, you may get H on first one, T on second one, T on third one which is indicated by HTT.

Like this, if you proceed checking for the possibilities, you would get 8 possibilities which are listed as follows.

HHH, HHT, HTH,THH, TTH,THT,HTT,TTT