At the top right of the screen tap on you name and tap Settings in the menu, then on the settings page tap Email accounts.
Email account settings is where you can add additional email addresses for use when sending email. By default the email address you sign in with will be listed here. You may want to add a generic info@ account, a ministry specific account like kids@ or maybe someone else's email account so that you can send email on their behalf.
Note: When you add additional email addresses an email will be sent to the email address to verify that you have permission to use this email address. When the email is received the recipients needs to click the confirm button in the email.