动词原型一般用在祈使句；一般现在时的复数人称或第一人称；或情态动词can,could,may,need,must等的后面.
如 don't touch me, let's go
I want to come back home. they need some book. I like it.
I can complete it.
过去式用在刚刚发生或过去某个时间点发生的动作
I comleted my homework this afternoon.
过去分词用在现在完成时,过去完成时,以及被动语态,定语修饰中的被动语态等情况下,如：
I have completed my homework.
I had completed my homework before I had dinner.
the baby was taken to my home(by...).
I like this book signed by the autho