Go to Settings > Scheduling.
You will see a list of your Holidays here. They are pre-populated when you sign up, depending on your account locale. If you are based in the US, Productive will add all US Holidays automatically.
Holidays will be taken into account when calculating capacity, and will be visible to your teammates in Scheduling and Time tracking as non working days.
If you scroll down a bit, you will see the events too.
You can add new events and mark them as either paid or unpaid. In both cases, scheduling people on events will track time for them automatically, during their absence. The different between paid and unpaid events is that the paid events will also apply the staff members' cost rate against the logged hours, while unpaid events won't.