How to use

if you have not yet created a iCloud account, sign into System Preferences (or Settings)>iCloud with your Apple ID. Check Mail in the checklist there, and any other data types you want to sync. You will be asked to create a new @icloud.com address.

Then go to your Mail application; you will see the iCloud account there in addition to any email accounts you already have. Access your mail there in the same way you do your existing emails.