After plugin is installed you have to start initialization process. You First, you have to be logged in to an administrator account first and then access "Add-ons" view(1).
There are two ways to do it. Either by clicking Configuration button in accessing Manage add-ons view view (2) and then clicking Configure (3) button. (note: button is localized located below Vacation Manager plugin name, cloaked inside a drop-down menu).
Alternatively by clicking Initialize Vacation Manager (4) link in the sidebar.
Now you should see first step view to define Vacation Manager project
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Next Vacation Manager core elements - Navigation Bar Menu [1.23.x]