For an organism, each character has two alleles, one inherited from their mother and one from their father. For most characters, there are two kinds of alleles. Dominant alleles are expressed as a capital letter and recessive alleles are expressed as a lowercase letter.
During formation of gametes, alleles are split so that only one of the two is expressed in each gamete. Mendel's Law of Separation states that if you had one recessive and one dominant allele for a specific character, then half your gametes would have one set of alleles while the other half had the other. Mendel's Law of Independent Assortment states that each set of alleles for a specific gene segregate independently from other sets of alleles into gametes.