Children dx with ASD have problems with in some or all of the areas of the "Triad of Impairment"
- Social communication
- Verbal and non-verbal language
- Repetitive or stereotyped behaviour
So a person with ASD may not understand that a conversation means input from both people, and will just ask questions without pause for the answer, or talk about something they like without noticing the other person's comments.
Those dx at the lower end of the spectrum may have little or no language at all, and be unable to communicate their basic needs. Further along the spectrum toward NT, you get people who have exceptional verbal skills with a huge vocabulary, but have no idea when to speak and when to listen, when the person they are talking to is bored, that water running out of the eyes means crying which means sad. They often don't know that smacking someone in the face hurts you - it just doesn't occur to them; but they know it gets them what they want!
Repetitive or stereotyped behaviours include stimming, echolalia, smearing, pica, lining up toys, having to keep things in certain places, rigidly sticking to rules, not being able to do school stuff at home and vv...
All this depends on the character of the person with an ASD dx. Everyone's different, especially people with SN 
Things like ADD, ADHD, ODD, OCD, Tourette's etc are often co-morbid with ASD, which is why there's such a cross-over.
HTH