1. When I came home last night, my parents (go) ..had gone... to bed.
=> We use past perfect tense to describe actions in the past that are completed at or before a give time in the past. In this sentence, "had gone to bed" are completed by the time the action " came home"
2. We don't know where (put) ..to put... this computer in my room.
=> We use "to V" in this situation to show a purpose or intention
3. I (not use) ..did not used... to get up early when i was small.
=> We use used to when we refer to things in the past which are no longer true. It can refer to repeated actions or to a state or situation: