Genki II Textbook (Although not technically free) is a great resource.
I am not confused much about the conjugation (される, etc),
but in identifying the who/what the subject is and what he is doing
(or what is being done by who).
(Everything down below is from Genki II)
Here's a way to remember it.
Causative
先生 は 学生 に 会話を覚えさせました。
("Director") は ("Cast") に ("Action").
The professor made the students memorize the dialogue.
The "director" decides what is allowed and what is to be done. Marked with は or が.
The "cast" performs the action. Usually goes with に.
The "action" is described with a causative form of the verb.
Passive
私 は 友達 に 車を使われました。
("Victim") は ("Villain") に ("Evil Act").
I had my car used by my friend.
In most passive sentences In most passive sentences, the "victim" has been unfavorably affected by the "villain's" act.
The one doing the action is the "villain", and the "victim" is affected in some way or another.
Here is an example where I think it is "not unfavorable", however the "victim" will still be affected.
このパッケージには、あらゆるものが含まれている。
Everything is included in this package.
("Everything" is "being included" by "the package".)
In this case, "Everything", or あらゆるもの, is the "victim", who is being affected by "being included".
"The package", or パッケージ, is the "villain" who is including "everything."
The reason why I don't consider this an "unfavorable" situation is because the sentence is about inanimate objects.
Causative-Passive
私 は 彼女 に 車を洗わされました。
("Puppet") は ("Puppet Master") に ("Action").
I was tricked by my girlfriend into washing her car.
The "puppet" is forced into performing an action. Marked with は or が.
The "puppet master" "wields power over, and manipulates", the "puppet". Uses に.
The "action" forced upon the "puppet" is described with a causative-passive verb.
