Time

The panel of the Time preferences is split into four tabs:

Date and time

A la izquierda, se puede configurar el día del mes simplemente clicando sobre él en el calendario. Puede cambiar el mes y el año clicando sobre él y usando las flechas (hacia arriba/ hacia abajo) hasta el correcto, o las teclas del cursor sobre el teclado.

Similarly, you set the time at the right. Or simply move the hands of the clock directly.

Time zone

Simply find and choose your country in the list of continents and press Set time zone. For countries with more than one time zone you'll have to expand one level deeper.
To the right you'll find the time of the currently set time zone and the preview time of the the zone you've chosen.

Also on the right side is a setting for the hardware clock of your computer. There are two modes for the clock:

Network time

Setting date and time manually is pretty much obsolete if you're connected to the internet. There are public servers that supply very exact time signals.

With the +/- buttons you can add/remove NTP-servers to/from the list.

The checkboxes below tell the system to Try all servers when synchronizing, not only the currently selected one, and to Synchronize at boot, so you can be sure you're clock always shows the correct time.

You can Reset to default server list if you accidentally deleted working NTP-servers and Synchronize your clock manually.

Clock

The last tab shows the options of the clock displayed in the Deskbar. You can disable the clock there completely with the top checkbox. The rest are equally self-explanatory.

In every tab is a button Revert that brings back the settings that were active when you started the Time preferences.