A basic grammar book explains this.

When can you use them? Whenever those tenses are correct for the idea you want to express... I think you need to think about it the other way around. Instead of 'I want to use this tense', think 'which tense should I use to express this idea in this situation?'. There are plenty of English learning resources that tell you how and when to use tenses. This forum is probably better for more specific questions.