The causative is similar to passive. It uses auxiliaries, but we focus on the fact that someone does something for you.
Ex: I'm having my car serviced at the moment has a typical causative structure .
SUBJECT + HAVE/GET something DONE
No need to say that HAVE/GET CAN take any tense whatsoever:
Different shades of meaning are possible:
You've had that explained often
I won't have the piano played by anybody.
3. result of past action
Other combinations of GET + PARTICIPLE.
GET somebody/something TO DO something means 'persuade' or 'manage to'
Ex: I got the children to sit and read the lesson.