The conditional explains what happens when one thing depends on another. For a real possible result, use if plus the present, then will plus the verb: If it rains, I will stay home. For an unreal present idea, use would: If I had time, I would help.
Would + verb is often used to make polite requests or offers, like “Would you help me?” It is softer and more polite than “will.” It can also describe a future action seen from the past, like “He said he would call.” After would, always use the base form of the verb.
Would have + past participle is used to talk about a past situation that was possible, but did not happen. It describes an unreal result in the past. We often use it with if. Example: If I had had time, I would have gone.