"Would" is talking about a hypothetical instance that generally will be coming in the future. For example: If you told me you were moving soon, I might say "I would help you move, but I'll be out of town that weekend". "Would have" is talking about a hypothetical instance in the past. So if you tell me how you played a softball game last weekend, I might say "I would have joined you, but I was feeling sick" Hope that helps!

They are both conditional verbs, but "would help" is a conditional present and "would have helped" is a conditional perfect. As Alex correctly says, they are both used for hypothetical situations, or in the past, something that didn't actually happen. You are particularly likely to encounter them as the consequence of "if" clauses relating to those situations, such as in these examples: - "If you came to visit [as you have not done so far], I would help you" -- this is about a present situation, extending into the future - "If you had come to visit [as you did not], I would have helped you" -- this is about a situation and its consequence in the past There is also a hybrid form, where the situation was in the past, but the consequence is still present: - "If you had come to visit [as you did not], I would help you [now]"

To add to Alex, I recommend that you study the conditional forms, particularly the second and the third conditional which are relevant to your sentences. Alex has given good examples of mixed conditionals however I suggest that you start with the standard conditional forms first and move on later to mixed conditionals.