Present unreal conditional with.什么意思?

Present unreal conditional with.什么意思?
下列四个句子是什么意思啊?
1.Present unreal conditional with unless,only if,and even of
2.Unless clauses include exceptions that would change the speaker's decision.
3.Only if clauses stress the condition for the result.
4.Even if clauses are followed by unxepected results.
谢谢啊!本人对英语学习很感兴趣!