The easiest way for me to describe my experience with Autism (Asperger's Syndrome in my case) from my own perspective:
I pursue my interests wholeheartedly, wanting to know as much as I can about them. Even though I enjoy interacting with other people, keeping up with the task of easily missed social cues and understanding group dynamics makes it exhausting. On top of social over stimulation, I also have to worry my senses in general, as I can easily be visually and audibly overwhelmed. If the stress I am put through becomes to much, I could have a meltdown, which means I must always be aware of my limits. Issues like this may be why I ultimately prefer spending large amounts of time by myself in a small familiar space versus out in the world where there are lots of people.
For me, this is my understanding for normal, my baseline to compare to how the rest of the world works. It is the way I have existed as long as I can remember. Of course, then I look around me and it's obvious that these are not the standards that most people live by, that the position I sit at to look at the rest of the world from is not the one most people hold. As a result, I have a harder time understanding the people around me than the average person probably does and the average person has a harder time understanding me than most people.
It's all obviously much more complicated than this, but that's the best I can do in a quick summary.