How do deaf people make a phone call?

They can use a State Relay Service where the Relay service works as an interperter by voicing what is being typed. They can also make video calls. This way they can sign to the person they want to talk to. 

Does sign language have grammar?

Yes it does.

How do deaf people know there is an ambulance coming when they are driving in a car?

Deaf people make use of their great vision. They see what is going on and then make room for the ambulance.

How do deaf people know someone is at their door?

Many people use doorbells that are attached to lights. This way when someone is at the door and ring the doorbell, the lights are turned on and they know someone is there.

How do deaf people wake up from an alarm?

They can use a vibrating alarm clock, which will wake them up. They can also use and alarm clock with bright flashing lights.