I realize I can use Outlook but it is easier to use the Mail App that came with the Surface 2. My problem is the emails in the inbox always delete after a day or so. Can't I make a change so I decide when to delete them?
You could try the "Download emails from" account setting. It may be that you have this set to only download 3 days worth of emails and I'm assuming any emails older than 3 days will be removed from the device (they shouldn't be deleted from your actual mailbox). That's how Windows Phone works, but I'm not entirely sure about the Win8 Mail App - it may work the same though.
This setting is a per email account setting. So edit the settings for the actual account in question.
If your problem is related to the fact that the Mail App is only downloading/syncing x number of days/weeks/months worth of emails - then you can set the "Download emails from" option to "Any time", which should download and then keep all your emails on the device.
As joeka said, you can adjust the window of time that the Mail app is set to display. The important thing to remember is that the Mail app is not deleting your messages, it's just showing you the messages from the time frame you set. All of your messages are still available either by changing the display period within Mail or using another client (Outlook, Web mail, etc.).