"To have someone do something" What does this really mean?

As a native Portuguese speaker, it's kind of hard for me to really understand what the structure "to have someone do something" means. For example in the following sentence:

I had him pick me up at school yesterday.

Would that be different from "He picked me up at school yesterday"? What is the difference?

Or for example: I'll have someone fix my car tomorrow.

Am I saying I'll pay someone to do that or I'm just saying someone is coming to do the job regardless of payment?

Solution 1:

NP₁ have NP₂ Infinitive VP is a causative construction.
(Note there is no to on the infinitive in this construction)

This construction means that NP₁ causes NP₂ to do whatever the infinitive Verb Phrase is.
So if the sentence is

• I had him pick me up at school today.

the meaning is that I arranged for him to pick me up at school today in some (unspecified) way.
And if it's

• I'll have someone fix my car tomorrow.

the speaker is committing to arranging for someone to fix their car.

Tomorrow can modify either will have (tomorrow is the day to arrange it), or it can
modify fix (tomorrow is the day to fix the car). This is what's called an "attachment ambiguity".