Welcome to the Apple Support Communities
You have three possibilities:
1. Open http://www.icloud.com, login with your Apple ID and choose Mail.
2. If you have Outlook, install iCloud Control Panel. Then, open Control Panel > Network and Internet > iCloud and tick Mail, so you will be able to access to your iCloud mail address on Outlook.
3. If you have a different mail program, set up your iCloud email address with this information > http://support.apple.com/kb/HT4864?viewlocale=en_US