There are 3 possible scenarios:
1. There are 2 heads coins
2. There is a heads coin and a tails coin
3. There are 2 tails coins
Next we eliminate those which dont fit the criteria of having "at least one coin is heads" and we are left with:
1. There are 2 heads coins
OR
2. There is a heads coin and a tails coin
The question does not give any information regarding order of the coins, therefore there is no "first" or "second" coin, there are only the sets which contain either 2 heads or a heads and a tails.
Probability= favourable outcomes/possible outcomes
Without the criteria of "at least one is heads" there would be 3 possible outcomes, and a 1/3 chance of both being heads, but after applying that criteria, it becomes impossible to land two tails coins. Thus we are left with one favourable outcome (both coins are heads) and two possible outcomes (both are heads OR one heads and one tails)
The probability of both coins being heads is 1/2