Switch to labels from folders. In other email programs, you might have stored email in folders. In Gmail, you use labels to categorize your email. Labels are like folders, but with a twist—you can apply several labels to an email, then later find the email by clicking any of its labels from the left panel. You can also search by label. Use ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.