I'm a 15 years old guy and I'm a bit shy and I don't have friends?

you could try joining some school clubs and activities they are a great way to make friends

Just be yourself honestly, go out try engaging in conversations with others. Choose a subject that you find relatable or know much about and see how that works. The only way you can go wrong is if you don't try at all.

• Start small. Being outgoing does not mean turning into a flamboyant extrovert or a busy socialite. Work on talking to individuals, one at a time. You could make a goal of starting a conversation with at least one person every time you attend a Christian meeting. Try to smile. Practice maintaining eye contact.
● Break the ice. ‘How?’ you might ask. Well, if you really have an interest in others, it’s usually not hard to find things to talk about. A youth in Spain named Jorge says: “I’ve noticed that simply asking others how they are doing or asking them about their work helps you to get to know them better.” A youth named Fred suggests: “If you don’t know what to say, just start asking people questions.” Of course, you don’t want people to feel that they are being interrogated. If a person seems resistant to answering questions, try sharing some information about yourself.
● Be a good listener. “Be swift about hearing, slow about speaking,” says the Bible. (James 1:19) After all, a conversation is an interchange—not a solo performance. So if you tend to be shy about talking, this may actually work to your advantage! People appreciate good listeners.
● Join in. Having mastered the art of one-on-one conversation, move on to talking in groups. Again, Christian meetings are an ideal place to acquire this skill. Sometimes the easiest way to get involved in a conversation is to join one that is already in progress. Of course, discernment and good manners are essential here. Don’t barge into what is obviously a private discussion. But when it is clear that a group is engaged in light conversation, try to become part of it. Be tactful; don’t interrupt and try to take control. Try listening for a while. As you get comfortable, you may be inclined to make a few comments.
● Don’t expect perfection of yourself. Sometimes youths worry too much about saying the wrong thing.
● Keep your sense of humor. Granted, putting your foot in your mouth is embarrassing. But as Fred observes, “if you just relax and laugh at yourself, the moment soon passes. You make a mountain out of a molehill when you allow yourself to get flustered, frustrated, or worried.”
● Be patient. Realize that not everyone will respond immediately. An uncomfortable lapse in conversation doesn’t necessarily mean that the person doesn’t like you or that you should give up trying to talk. Sometimes people are merely preoccupied—or shy like you. In such situations, it may help to give the person a bit more time to warm up to you.
● Try talking to adults. Sometimes adults, especially mature Christians, are quite sympathetic toward youths who are battling shyness. So don’t be afraid to try to start a conversation with an older person. Says Kate: “I can relax around adults because I know adults won’t judge me, ridicule me, or give me a hard time like kids my age might.”
Jesus stated another profound truth that may help you cope with loneliness: “There is more happiness in giving than there is in receiving.” (Acts 20:35) If you give of your time to help others—a child with his homework or an elderly person with shopping or keeping his or her house or garden neat—you will feel happier and perhaps begin a genuine friendship.