In simple terms, being gay means that you are sexually attracted to members of your own sex and that you identify with other gay people or the larger gay community.
Sexuality is a term used to describe a whole range of feelings, desires and actions relating to sex.
Nobody knows for sure why some of us are gay and some of us are not. Lots of theories have been put forward ranging from genetic differences to overbearing parents. The evidence so far suggests that random genetic factors play a part in determining our sexuality in the same way they play a part in determining, for example, lefthandedness. One thing we do know is that no-one chooses their sexuality. Some gay people knew they were different, if not gay, from as young as five or six.