Gmail provides an Archive function, which is for the case of you want to “clean up” inbox but you do not want to delete emails.
When you archive an email in Gmail (right click on an email), the email will “disappear” from Inbox, but it actually is moved to a label called “All Mail”:
1: If you want to see an archived email in Gmail, the most simple method is searching it. Just input any keyword about your archived email and search, you can search out all archived emails which match searching keywords.
There is another way: Since all archived emails are actually moved to All Mail label, so you can find the archived emails from the label “All Mail”. Click More labels from left panel, you can see the All Mail label. Click All Mail label you can see your all emails include archived emails