How do I mark somebody on leave?

Open Schedule, then This week. Press the cell for that person on that day, the same cell you use to put them on a job.
Choose On annual leave, Off sick, At TAFE, On an RDO, Public holiday, or Not working other. Use Not working other for something like a vehicle service. These are under the jobs in the same list.
YourCA records it when you press. A day off is the whole day and has no hours. So YourCA does not ask for hours, and never shows the rostering form for a day off.
YourCA records the day against the person and against no job. So it shows on every week, including the week of a single job. That is deliberate: you need to see that somebody is away on the job you were about to put them on.
For part of a day, mark the day off first. Then press Another job on the same cell, and put them on the job for the rest of the day.
While you do this, YourCA asks for the hours of the day off, so the two entries do not both read as the whole day.
If somebody is already off and you pick a different reason, YourCA changes the reason. It does not add a second one.
To put them back on a job, press the same cell and choose the job. To clear the day completely, choose Not on.

Worth knowing

A day off does not count in the number of people under that day. It never shows as a missed clock-on, and never causes a double booking. Those three are why you record it this way, and not as a job called Leave. A job called Leave would also count as an active job, and you would be billed for it. This does NOT approve anything. There is no leave balance, nothing accrues, and no entitlement is worked out. It records that you rostered somebody off. Payroll holds the rest.