I am confused with following question. What's the difference between たべられる and たべさせられる?
食べる "to eat (something)" (active voice)
食べられる "to be eaten (by someone)" (passive voice)
食べさせる "to make/let (someone) eat (something)" (active voice, causative)
As you might know, the passive voice can sometimes express a feeling of unhappiness towards the result of the action (that is done against one's will).
In this case, the one doing the action of the verb is always doing it against his will, forced by someone.
Hence, 食べさせられる means "to be forced (by someone) to eat (something)".
I ate the cake.
The cake has been eaten by me. ← Unnatural because of the inanimate subject
I made/let my little brother eat the cake.
My big brother made me eat the cake. / I've been forced by my big brother to eat the cake.
I had to wait my friend for a good hour. / My friend made me wait a good hour.
For the Godan verbs, される is often used instead of せられる:
待つ → 待たせられる → 待たされる