By default, new campaigns are set to Preview. If a campaign has been set to a different status you will need to change the status back to Preview by clicking the Change Status drop down on the same row as the Campaign Name. Once a campaign is in Preview you can go to the web page associated with that tour and the campaign should start.
Be aware that multiple campaigns on the same page will only show the campaign with the highest priority, which is the top most campaign.
You can re-order campaigns by clicking and draging the campaign name up or down the list.