I would ask the pre-school teachers to clarify their concerns. They may have experience in this area. Ask for their advice.
When a child's speech is delayed, speech therapists can suggest simple quick activities you can do to help your child catch up. Speech difficulties are better helped when the child is younger rather than older.
If a pre-school child's speech is delayed, it is better for intervention to happen at the pre-school stage. Then a child can be given the help he needs. His speech will catch up and then he will be able to access the learning at school.

Many pre-school boys have problems sitting still and with speech. If the teachers are especially concerned about your child, ask why, then take it from there.
If it is your first child, it is hard to know what to expect in terms of behaviour and development. If your son finds it more difficult to sit still etc, the pre-school should be able to help him develop concentration etc. Don't worry too much now, just find out what the pre-school teachers' concerns are based upon.