Requesting Help with Identifying Grammatical Structures

  1. They will be requesting help
  2. They were requesting help
  3. They have requested help
  4. They had requested help
  5. They requested help
  6. Because of the climate, the Atacama desert in chile is visited by only the hardest trekkers
  7. Leaving the ice-cream out on the ledge was not a wise idea.

Could anyone please help me with this or point me to resources that could help me? I'm quite baffled.