Archive mail

Archiving lets you tidy up your inbox by moving messages from your inbox into your All Mail label, so you don't have to delete anything. It's like moving something into a filing cabinet for safekeeping, rather than putting it in the trash can.
Any message you've archived can be found by clicking the "All Mail" label on the left side of your Gmail page. You can also find a message you've archived by clicking on any other labels you've applied to it, or by searching for it.

When someone responds to a message you've archived, the conversation containing that message will reappear in your inbox.
To archive messages:

1. In your inbox, select the message by checking the box next to the sender's name.
2. Click the Archive button in the toolbar above your message list.
   (If you have a message open, you can also archive it by clicking the Archive button above the message.

To move an archived message back to your inbox, follow these steps:

1. Click All Mail. (If you don't see All Mail along the left side of your Gmail page, click the More drop-down menu at the bottom of your labels list.)
2. Check the box next to the sender's name.
3. Click the Move to Inbox button.

credits;http://support.google.com/mail/bin/answer.py?hl=en&answer=6576