Go to Actions > Leave (dropdown menu) > Create leave request. Complete the short leave form and click Add. Initially the leave request will be created and checked against Absence rules but will be for your eyes only (in draft). This give you a chance to review the request and check everything is as you expect before clicking the 'Send for approval' button.
If your absence rules allow it, you can edit the exact hours you require, say for a half day or an hour in the morning for a personal appointment by clicking Change next to the Duration or clicking Change Leave Days under 'Leave Request Days'. Adjust the hours as required. In order to remove a period altogether change the hours to 00:00.