You can easily add a site to Uptime Monitoring from the site list in Sync. Click the "+" beneath Uptime to the right of the site you wish to add.
You can also add a site by navigating to the Uptime page. Click the Add New button and then select the sites you would like to add. Click the Add to Monitored List button and refresh the page to view the sites in the Uptime list.
Viewing Uptime History
You can view a site's total and recent Uptime history by clicking the down arrow to the left of a monitored site.