The Microsoft Mail app is really useful and easy app. It is a replacement for the Windows Live Mail and is quite beautiful. The only thing it lacks: it does not support drag and drop.
Steps to add an email account
1. Click on the Mail tile on the Home screen. If the tile is missing then open the Charms bar, select Search and type mail. Next, click on the mail icon.
2. Next, sign in with your microsoft account. If you do not have any microsoft account like hotmail, live, outlook then you might have to click Signup and create one. If you already have it then type your email address and password. Next, click on the Sign in button.
3. Next, if you are asked with security info like phone nuber and alternate email then provide it and click on the Next button.
4. Next, your email inbox is shown. If you want to add other email accounts like gmail, outlook then click on the Add email accounts at the bottom of the page. And provide your login info on next screen. That are the complete steps to add an email account to Windows 8.
In earlier Windows 8 version i.e. developer preview you would find add new accounts options in the first mail setting screen but it is gone in Windows 8 consumer preview. First of all you must configure Microsoft account (atleast one microsoft account like hotmail, live etc is required) to add other accounts like gmail etc.