Many people with autism are also under or over sensitive to light, noise, heat, touch, taste or smell. These difficulties can have a big effect on how people with autism experience the world. If you are not affected by any of these difficulties, it can sometimes be hard to imagine how they must be feeling. For many, it can be very upsetting and even scary.
Imagine you are at the movies and you have someone talking behind you, someone's mobile phone ringing in front of you, someone chewing popcorn next to you, some one with really smelly shoes, and someone with a bright hat on in the front row - it would be hard to concentrate on what's going on in the movie, wouldn't it? That's how people with autism feel a lot of the time.
People with autism also dislike change. We all in many ways don't like change but as you and I may understand that changes happen all the time and we get used to them, this is something that people with autism can find really hard. With all the difficulties I explained earlier, the world can seem a very scary place for someone with autism. So, when things are the same it makes them feel a little safer because they know what is going to happen but when something changes, it takes some of that security away.
So, if you think about the example of being at the movies, you can start to see why they stick to things they know and don't like new things sometimes. If changes are going to happen, it can help to give the person as much warning as possible so that they can prepare for this.
The person with autism that you know might also show some odd behaviours such as flicking their fingers, flapping their hands or arms, spinning or jumping. Not everyone with autism will do these things but those that do, will do them for different reasons. Some people may do these things to make them feel happy and possibly just like the feeling they get from doing it, whereas others might do these when they are worried about something. For some people, it helps them cope with what's going on around them.
Many people with autism can also have an obsession with a particular thing. For example, my brother, Ben, likes dinosaurs and can talk about them all day if we let him.
I hope this has helped you understand what autism is. But remember, everybody with autism is different so the person you know with autism may not show their difficulties in the same way that my brother does.
You may also like to read some real-life stories from siblings.