Firstly, please look at the amendments I have made to your post. There is no need to use any kind of salutation, especially something like "seniors and juniors" which means nothing to us. Make sure you use standard English words when using the forum (not "wanna", for example).
Your question is far too broad to be dealt with here. We do not replace grammar books or your own research and study. If you have a specific question about a sentence with "could" or "would" in it, then feel free to post it here and we will endeavour to answer it. We don't provide the examples - you do.
Student or Learner