这个视频主要介绍了树的重要作用并涉及到一些单词和词组的运用，如absorb, emit, CO2, O2, biodiversity, species, deforest, the last thing等等。

This video mainly covers the introduction on the importance of forests and trees and it also involves some use of words and phrases like absorb, emit, CO2, O2, biodiversity, species, deforest, the last thing.