Your employees can request annual leave once they're setup with a login. However, you can also add Leave retrospectively if you need to.
To do that, open up the Leave page and click the blue plus button at the top. You'll be presented with the 'Add Leave' form
Fill in the details and click 'Add Leave'.
You'll be taken back to the Leave page where you can see a yearly overview of all the annual leave that's been scheduled.
Click on a month to expand it and view a timeline of all the Leave records for that month.