Causative verbs show that somebody/something is indirectly responsible for an action. The subject doesn't perform the action itself, but causes someone/something else to do it instead. For example:
- Yesterday I had my hair cut.
I didn't cut my own hair, but I made someone else do it for me instead - I "caused" them to cut my hair.

Have is a common causative verb. Instead of doing something ourselves, we "have" someone else do it instead. It has the following form:
The verb "to have" + object + past participle. For example:
- I had my jacket cleaned yesterday.
- Did you have your computer fixed?

Sometimes we use have as a causative verb when we intend to perform the action ourselves. For example:
- When will the report be ready? I'll do it by tomorrow morning. >>
- When will the report be ready? I'll have it done by tomorrow morning.

By using the causative the second sentence takes attention away from the doer of the action, and gives more attention to the action being done. It sounds polite and professional.

Get is often used instead of have. For example:
- I got my computer fixed - I had my computer fixed. These two sentences mean the same thing.
- I got my jacket cleane. - I had my jacket cleaned. These two sentences mean the same thing.

Causative verbs are often used with negative experiences. In these situations it's more common to use have. For example:
- I had my wallet stolen. (I didn't actually cause my wallet to be stolen - someone stole my wallet from me)
- She had her window smashed.

For more information on Causative verbs see:

-----