Hi. I need to learn as much as I can about autism. My cousin is autistic and I want to be better able to understand him. 
Hi there. Autism is an unfortunate birth defect that is commonly associated with troubled social interaction and communication.
Are there different kind of autism? And are there differing degrees of severity?
There is. One of the more known ones is Asperger Syndrome. Aspergers makes it almost impossible to interact whatsoever with anyone. 
My cousin interacts fairly well, but he struggles with it. How common is autism in the general population?
I am not 100% sure on how common it is, but to answer your previous question yes there are differing degrees of it.
I think it seems like autistic people often have gifts or special talents in specific areas, too, like my cousin is excellent at music.
Autism
Autism is a developmental disorder characterized by difficulties with social interaction and communication, and by restricted and repetitive behavior. Parents usually notice signs during the first three years of their child's life. These signs often develop gradually, though some children with autism reach their developmental milestones at a normal pace before worsening.
Autism is associated with a combination of genetic and environmental factors. Risk factors during pregnancy include certain infections, such as rubella, toxins including valproic acid, alcohol, cocaine, pesticides and air pollution, fetal
they will have a manageable degree of sensory stimuli, which will make them calmer, better able to process the sensory stimulation they receive, and better able to relate to others.
Overview Communication and social interaction.
Organizations interested in spreading awareness about autism and how to be autism friendly, such as The Autism Directory, have created training programs for communities to illustrate how people with autism may communicate or interact differently from neurotypical people, or people without autism. There are also suggestions for how to modify one's reaction to improve