You're new here. Is this homework? We don't do homework. I'll give you a hint. How many possible tosses can you get with one coin? 2 How many possibilites do you have with 2 coins? 2 with the first, two with the seconds, so overall you've got? Now follow that chain of logic out to seven coins. Now how many possibilites are there to NOT have at least two heads? That would mean you could only have ONE head. How many possibilities are there for that? Subtract that from the total number, and you've got your answer.
If you toss seven fair coins, in how many ways can you obtain at least two tails?