Sometimes you just need the basics to get you started. What is autism? NIH offers a basic overview page.
Here are some things autism is not:
Autism is not schizophrenia. However, I feel people should also be aware of schizophrenia, there are a lot of ugly myths abounding about it.
Autism is not bad parenting.
Autism is not mercury poisoning. No, it isn't. The symptoms do not match up. (However, I do recommend having your pediatrician check for heavy metal toxicity if you are concerned. There are valid tests for it, and valid treatments for it.)