My ‘search email’ function will not find emails

I know these emails are in my in my inbox. I have looked at the forums without success and followed what little advice there was. I want to know how I can easily fix this problem. I want to know in plain english, not being kept referred to links that don't help. I have cleared the cache, I do not have thousands of emails in my boxes either. I am getting desperate to find these 'hidden' emails. Thanks.