Question

i dont know how to do probability

Answer 1

Okay. So there's 100 percent chance you don't know what you're doing.

Answer 2

Many events can't be predicted with total certainty. The best we can do is say how likely they are to happen, using the idea of probability.
When a coin is tossed, there are two possible outcomes:

heads (H) or
tails (T)
We say that the probability of the coin landing H is ½.

And the probability of the coin landing T is ½.