3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo

Gametes are sex cells: the male one being sperm; the female one being an egg.
When they join together it is know as fertilisation. At this point the fused gametes become a zygote.
A the zygot then divides repeatedly, at this stage it becomes an embryo.