You can insert a link into your campaign that when clicked on will open a webpage with with contact's version of the email displayed.
The option to add links (hyperlinks) appears on the ribbon whenever you are working on text or images. When adding links to text, first type the text into your email, then select that text before clicking the Link button and choose View in browser from the menu of the window that pops up.

A View in browser link can have the following aspects set in the Add a link screen:
The text preview shows how this link will appear in the campaign.