Autistic people vary enormously from each other but they all have impaired communication skills of one kind or another.
Those communication skills include verbal skills (such as speaking and listening) and non-verbal skills (such as making eye contact).
For example, some autistic people:
Cannot speak, can only use a few words or learn to speak very late
Speak using unusual volume, pitch, intonation, rate, or rhythm
Use odd language or repeat the same things over and over again
Find it difficult to hold a two-way conversation i.e. where each person speaks and then listens to the other person
Find it difficult to explain how they feel using words, expressions, tone of voice, and gestures
However some autistic people claim that, rather than having poor communication skills, they have different communication skills and that non-autistic people need to learn how to communicate using those skills.
Please see our detailed entry on Social Communication and Autism