[let + person + verb]
This construction means "to allow someone to do something."
John let me drive his new car.
Will your parents let you go to the party?
I don't know if my boss will let me take the day off.
[make + person + verb]
This construction means "to force someone to do something."
My teacher made me apologize for what I had said.
Did somebody make you wear that ugly hat?
She made her children do their homework.
[have + person + verb]
This construction means "to give someone the responsibility to do something."
Dr. Smith had his nurse take the patient's temperature.
Please have your secretary fax me the information.
I had the mechanic check the brakes.
[get + person + to + verb]
This construction usually means "to convince to do something" or "to trick someone into doing something."
Susie got her son to take the medicine even though it tasted terrible.
How can parents get their children to read more?
The government TV commercials are trying to get people to stop smoking.
Get vs. Have
Sometimes "get someone to do something" is interchangeable with "have someone do something," but these expressions do not mean exactly the same thing.
I got the mechanic to check my brakes.
At first the mechanic didn't think it was necessary, but I convinced him to check the brakes.
I had the mechanic check my brakes.
I asked the mechanic to check the brakes.