Gametes are the cells in human body used for reproduction, such as sperms or eggs, and somatic cells are the other body cells, such as muscle cells, skin cells and all other.
First, they have different number of chromosomes. Gametes have only one set of chromosomes, while somatic cells have a complete 2 set of chromosomes. This is because fertilization requires 2 gametes joining together and this will help maintain the correct amount of chromosomes at last.
Second difference between them is that gametes are products of meiosis, while somatic cells are products from mitosis. Both are types of cell divisions but meiosis produces 4 genetically different cells while mitosis produces 2 genetically indentical daughter cells.