If you feel comfortable with HTML you can write your HTML code directly into the OFFER field as I did. If you want to include images don't forget to make them available through a public web folder. In this example I used the Google logo.
As you may also have noticed I hard coded the UNSUBSCRIBE e-mail address link. There is an explanation for that. Normally one would simply write a regular unsubscribe text and then select that text and hit the UNSUBSCRIBE button available when seting up the new e-mail activity. However if you set the FROM field to a Queue (as I did) your unsubscribe e-mail link will be broken to "mailto:[Run_Time_Address]?subject=[Run_Time_Subject]". After a lot of testing I gave up of this feature and decided to hard code the unsubscribe text/link. Doing this I'm also sure to include the unsubscribe text/link. I should warn you that the unsubscribe e-mail To should be the Queue's e-mail and the subject should be "UNSUBSCRIBE: E-mail Activity Subject". It's very important to match the UNSUBSCRIBE subject with the e-mail activity subject or the CRM won't be able to connect the unsubscribe request with the campaign in order to automatically create a campaign response and set sender's Send Marketing Materials = NO.
I will write a specific post about How to send e-mail campaigns from queues because I have some useful tips and tricks for you.