open my icloud email

Sign in with the Apple ID and password at www.icloud.com on a web browser and then follow the steps in the article https://support.apple.com/kb/ph2638?locale=en_US

Have you signed in in System Preferences>iCloud and enabled Email? Presumably you've tried https://www.icloud.com, signing in and going to the Mail page? What happens when you try? What sort of computer are you using, and what operating system?