Great question! There are many ways in which gametes different from the other cells of the body - the cells that we call "somatic." Think about what a gamete has to do that is different than what most other cells do and you will start to uncover many of the cellular differences. For example, gametes have to become haploid - they have to reduce their genetic material to a single copy, while somatic cells are diploid. Gametes go through a process of genetic reduction called meiosis - and only gametes do this. Also, the gametes carry all of the genetic information onto the next generation and so their DNA is somewhat "protected" compared to that of somatic cells. Further, gametes - in particular, the oocytes -- are able to give rise to an entirely new organism. No other somatic ell (that we know of) is able to do this naturally (though some stem cell research is focused on addressing this issue). There are many other differences as well, but these ought to get you started. Again, think about relating function -- what the cells do -- to their form.