It's time to learn English,

1. The first sentence

Just because you're unhappy doesn't mean that you can take it out on me.

1.1 The translation of the first sentence

你心里不舒服，并不表示你可以拿我出气

1.2 The summary from the first sentence

one： Just because XX doesn't mean XX （就因为...也不代表...）
two： Take it out on XX （拿 XX 出气）

2. The second sentence

What's done is done. It's time to move on.

2.1 The translation of the second sentence

过去的已经过去了，现在是向前看的时候了

2.2 The summary from the second sentence

one：It's what's done （就是这么做的）
two：It‘s time to do sth （是时候做某事了）
three：What done is done （木已成舟，无法挽回）

3.The third sentence

It is important for we young people to know what should be done or not.

3.1 The translation of the third sentence

对我们年轻人来说，了解什么该做，什么不该做是重要的

3.2 The summary from the third sentence

one：It is important for sb to do sth （对某人来说做某事是重要的）
two：It's what's should be done （应该这样做）