Press the Windows key and search for the app "alarms" on the start screen. You can just start writing the first letters of the program name, and the search he will find the right tile.
In the menu you can configure various reminders and alarms. For example, if you wish not to miss the end of the day, set the alarm for 18-00. For this outer circle adjust the minutes, and the internal clock. To go from 12 hours to 0-00 just need to make a turnover inner circle.
To set an alarm on desired days of the week, just put a tick in the "On days". If days is not specified, the alarm will trigger only once.
When the alarm goes off, you can snooze for 9 minutes or just stop it by pressing the "Close"button.
The clock will only work if the laptop or computer will be enabled. In sleep mode the alarm will sound only on tablets running Windows 8.1.
Similarly, you can set the alarm clock on the computer running Windows 8.1.