From the Share & Assign, you can ‘Send Email’ to the selected record.
By clicking on that action button, it would prompt user to select an email template. 
The email templates list would have list of all the templates that are created within the CRM and custom templates as well. You may select from the list or select New email to create a new one. Selecting template would directly perform the mail action if email id is available. While creating a new one would redirect to CRM email screen. 
Note: If user to whom the mail is being sent is not operating the email address, then the mail won’t be sent and an error message stating that record’s email address is not active will be displayed.