By default, new engagements are set to Preview. If an engagement 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 engagement Name. Once an engagement is in Preview you can go to the web page associated with that tour and the engagement should start.
Be aware that multiple engagements on the same page will only show the engagement with the highest priority, which is the top most engagement.
You can re-order engagements by clicking and dragging the engagement name up or down the list.