It is a good practice that before sending bulk email (group send), the same message is sent to a test contact through quick send, just to make sure that the mail content is fine. 

Quick send
Compose Mail >>> Quick Send >>> Select sender Email >>> Add the subject line >>> Enter EmailID (max 5) >>> Select the template (Emailer design) >>> Send mail

Group send
Compose Mail >>> Group Send >>> Select sender Email >>> Select Contact list >>> Add the subject line >>> Select the template >>> Send mail