Well let’s draw a punnet square. So first make your four boxes. Now, heterozygous means having two different alleles of a particular gene. We’re going to use the letter ‘A’, but you can use any letter. In your first box there will be the dominant alleles. This can be identified as ‘AA’. A dominant allele is capitalized (A). A recessive allele is lower case (a). So in the first box it will be AA. Move over to the box on the right it will be Aa. Move down one box (on the right side) that will be aa. Now still on the bottom box, move over one to the left. That will be Aa. Since hetero means different, the heterozygous alleles would be Aa which means you have 2/4 probability of the child being affected. So 1/2.
