Adverbs of probability tell us the likelihood of something happening.
If you imagine playing dice, what's the likelihood (probability) of rolling a six? It's possible, but it's not certain. You'll certainly throw something between one and six, but your not likely to throw two sixes.
Adverbs of probability include; certainly, definitely, doubtless, maybe, perhaps, possibly, probably etc.
We will win the game. = We will certainly win the game. - In this sentence certainly shows us the probability.