Could you be a bit more specific so that we know where to start? I assume you've read various explanations in grammar books? Are there parts of those explanations that you don't understand?
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PicnicThose parts where they explain how to use IF correctly.I don't want to prejudice anyone else's answer, but, for me, explaining the entire use of "if" from scratch is too much work to expect anyone to do at this forum. I would recommend that you identify specific usage patterns that you don't understand and ask about them individually.