In a passive-voice sentence, make the object of the sentence the subject and don't worry too much about who did the action. For instance, let's take the sentence: "He did his homework." In the passive voice, this would become "His homework was done." Alternatively, let's try "The mother lugged the child." In the passive, it changes to "The child was hugged by the mother."
Korean verbs are changed to the passive voice by adding 이, 히, 리, or 기 to the verb stem. Which syllable you add usually depends on the letter the verb ends with; however, there are many exceptions to this rule and you simply have to memorize most of the words.
Verbs ending in vowels or ㅎ normally have 이 added.
보다 (to see) > 보이다 (to be showing/seen)
쌓다 (to pile) > 쌓이다 (to be piled up)
놓다 (to put) > 놓이다 (to be put)
바꾸다 (to changed) > 바뀌다 (to be changed)
Verbs ending in ㅂ, ㄷ or ㄱ take 히.
잡다 (to catch) > 잡히다 (to be caught)
읽다 (to read) > 읽히다 (to be read)
먹다 (to eat) > 먹히다 (to be eaten)
닫다 (to close) > 닫히다 (to be closed)
Verbs ending in ㄹ almost always take 리.
걸다 (to hang) > 걸리다 (to be hung)
열다 (to open) > 열리다 (to be opened)
듣다 (to listen) > 들리다 (to be heared)
밀다 (to push) > 밀리다 (to be pushed)
Verbs ending in ㄴ, ㅁ, ㅅ or ㅊ take 기.
안다 (to hug) > 안기다 (to be hugged)
끊다 (to stop) > 끊기다 (to be stopped)
쫓다 (to chase) > 쫓기다 (to be chased)
담다 (to put something in) > 담기다 (to be put in)
When an active verb ends in 하다, you can change it to passive simply by changing 하다 to 되다.
사용하다 (to use) > 사용되다 (to be used)
준비하다 (to prepare) > 준비되다 (to be prepared/ready)
In the passive voice, "The child was dressed by the mother."; in the causative voice, "The mother dressed the child. Korean uses almost exactly the same particles for this as it does for passives. They are 이, 히, 리 and 기. For causatives you also sometimes need 우 and 추.