I helped him do / to do it.
I was helped to do it. - passive
Causative verbs designate the action necessary to cause another action to happen. In "The devil made me do it." the verb "made" causes the "do" to happen. Here is a brief list of causative verbs, in no particular order: let, help, allow, have, require, allow, motivate, get, make, convince, hire, assist, encourage, permit, employ, force. Most of them are followed by an object (noun or pronoun) followed by an infinitive: "She allows her pet cockatiel to perch on the windowsill. She hired a carpenter to build a new birdcage."
Three causative verbs are exceptions to the pattern described above. Instead of being followed by a noun/pronoun and an infinitive, the causative verbs have, make and let are followed by a noun/pronoun and the base form of the verb (which is actually an infinitive with the "to" left off).
* Professor Villa had her students read four short novels in one week.
* She also made them read five plays in one week.
* However, she let them skip the final exam.
Verbs and Verbals
The verbs mostly used as causatives are get, let, have and make.
Note: 'get' follows the pattern: Get someone *TO* do something.
ENGLISH PAGE - Let / Make / Have / Get
The idea is that help can be used either with the particle to or without to. When used in passive constructions, help is followed by to:
He had been helped to do it.
She was helped to do it.
Here are some useful links: