Open Google Contacts from a new email
Click To or Cc in a new email to access a searchable list of your Google Contacts
When composing a new email in Gmail, you can either start typing an email address and wait for the dropdown list to show the best 10 matches, or you can use this tip.
Click on To and a pop up box will open showing your Google Contacts list. You can search for contacts and see more than your top ten matches, or you can browse through your Contacts Groups. Once you have found the person you want to email, click on the name to add them to the To box. Multiple contacts can be added in this way - and there is an option to create a Contacts Group if these are people you email frequently.
You can use this to add Cc and Bcc contacts as well, simply click the Cc or Bcc text when composing an email.