If this is the first time you have run the email app, you will be presented with the new account wizard with a selection of email providers.
If this is not the first time, tap and then tap and then tap Add Account
Tap on the email provider for your account.
Enter your email address and password.
Tap on Next
Your email account will be setup and then you are finished!
Notes
Your phone must be connected to the internet via WiFi or 3G in order to create your account.
The email app doesn't allow you to create a new email account. It only allows you to add an existing email account. If you need a new email account, please create a new account at your email provider's website before adding it to the email app.
Only certain email providers are supported. Please see the Firefox OS FAQ for the official list of supported email providers.