If you have to send emails that have a certain pattern to be followed, then you can save them as templates.
Eg. You have to send an invitation mail to your friends.

• First fill in a subject line ‘You are invited to my party’
• Write out the details: Dear _____,
  We are having a party at my place, sharp 7.30. Be there on time. The gang is coming too!!
  
  Regards
  Buddy
  
  
• Go to ‘Save Mail As’ > ‘Templates’.
• Now whenever you want to write an invitation, simply click on ‘Templates’ and choose the template.
  Add the name as per requirement. Time saved!
• You can also add an attachment in the template.

Draft means an unfinished email that can be stored for further editing.
To save a draft, you can click on 'Save Mail As' > ‘Draft’. These saved emails are stored in a folder called 'Draft' and can be sent at any time. You can also add more content to the mail, if needed. Note: Attachments also get saved when an email is saved as a draft.