Some autistics are considered nonverbal, meaning they may not speak or they may have limited verbal communication abilities. The question we need to ask ourselves is, "Can they communicate with others," and if the answer is yes then what does that look like.
Communication can be written, sign language, and by other nonverbal means such as an augmentive communicate device (such as a special tablet). Also, hugs, kisses, thumbs up and high fives are forms of nonverbal communication. Your child will need support by a professional to learn to communicate effectively verbally or otherwise.
Some autistic children have a delay in the area of speech. If your child has a speech delay then you should seek therapeutic intervention from a licensed Speech Language Pathologist. Do not be afraid to ask questions regarding how you can assist the therapist between sessions, you should be allowed to be present during therapy sessions, and you should be informed of progress and goals therapy goals.
There are a number of speech therapy providers, so please do not waste time on a wait list of months or even years without seeking support elsewhere. Early intervention of speech therapy is critical to supporting your child's development. Therefore, your child will need to be receiving treatment as soon as possible.
It is important to pay attention to your child to learn how they communicate because it may not be the typical way of communicating. Screaming could be your child communicating fear, anger frustration, pain etc. My son was 4 when he started screaming. He had emerging speech and when he would run out of words to communicate, he would scream. I learned it was my job to figure out why he was screaming. I started asking him if he was mad, sad, angry, etc until he would say what was wrong, "I angry" or "I sad". It may take time to understand the source of the frustration so be patient and keep trying because as difficult as it is for you to understand your child is working hard to be understood too.
Don't give up on your child who may be nonverbal because he or she is learning everyday from you. The best thing you can do is read and talk to your child. They are soaking up all your communication so keep working with them. Also, it is important to model good communication skills too because your child is always listening and watching you. It may be difficult, but with time your child will be able to communicate effectively.