Many of the emails in the Account Designer look similar but the situations that trigger them are what are specifically different:

Reset Password Email: This is triggered when a GIFTS Online user resets a grantee's password in the IGAM (Application) module
Password Reminder Email: This is triggered when a grantee clicks 'Forgot Password' in the applicant portal 
Password Update Email: This is sent to a grantee after they manually change the password once logged into the applicant portal
Create Account: This is triggered when a GIFTS Online user creates or transfers an account to a new user in the IGAM (Application) module
New Account: This is triggered when a grantee clicks 'New Applicant' in the applicant portal