how to set sync for email in real time

First, you need an email provider that supports Push. Then you need to enable Push in Settings/Mail,Contacts,Calendars. Push is supported by iCloud, by MS Exchange accounts, gmail, Yahoo, AOL and premium Hotmail/Windows Live, plus a few others. No POP3 email providers support Push. If yours doesn't you will have to set a value to check for mail in the email settings.

Google has a gmail app that will push. They used to support MS Exchange, but dropped it except for corporate accounts.