I have told all my friends i have because they have.
Hi there and thanks for your question.
Most 13 year olds have not had sex. There is very good research that tells us that only about a quarter of 16 year olds have had sex (meaning that most haven't) and only about half of 18 year olds have had sex. So, you are very normal and actually in the majority!
Some of your friends may be doing the same thing as you and saying they have had sex when they haven't. That's pretty common. Or it may just be that your friends are having sex earlier than most other people.
Your question about how to have sex is a big question and it's not really possible to answer it fully here, but I'll give you a short answer. "Sex" usually means sexual intercourse or penetrative sex. This means penis in vagina sex for a heterosexual person. For this to happen, the guy's penis needs to be erect (hard). Then the guy and girl will usually move the penis in the vagina in a way that feels good until the guy ejaculates. Ejaculation means that a fluid called semen comes out of the penis. This fluid has sperm in it, which is what can fertilise an egg and make a girl or woman pregnant.
That was a summary—there is a lot more to sex than that. There is foreplay and other ways people can touch and pleasure each other, and importantly there is also the relationship with the other person, and all the feelings and emotions we have to do with sex.
Deciding that you are ready to have sex for the first time is a big decision and something only you can decide. There is no rush. It's important to wait until you are really ready, and then to make sure that you are doing it because you want to, in a way that you want to, and with a person you want to do it with. Also, if or when you do get to that stage and decide you are ready, remember to use a condom every time to protect yourself from sexually transmissible infections (STIs) and unplanned pregnancy.
Have a look at the UK links below for more information about sex. All the best and take care.