To use the time clock, select this button in the top-right corner of the screen:
Upon selecting this, the time clock will appear like this:
There, you can adjust your start time, select your category add an optional note and select the submit button.
When recording the end time, the start time will be greyed out and you can enter the same information.
To adjust the category list, select the gear icon:
There you can add/edit categories that will populate the category list.