Organ/Playing the Manuals< Organ
If you're already familiar with how to play keyboards, then playing on the manuals should pose no difficulty for you. Bear in mind though, that dynamics are not controlled by how hard you strike they keys (like on a piano). Organ technique and fingerings also vary differently from other, stringed keyboard instruments because there is no "decay" after you press and hold a note. This allows for more finger substitution.
Depending on what type of organ you have available, the action may be electrical or manual (called tracker action). If it's the former, then the keys should be fairly easy to press, but if it's the former, depending on construction and age, the keyboard may have a very heavy, deep action and you may have to adjust your playing style accordingly to accommodate for it.
Almost all organs have two manuals or more. As said previously, they operate different pipes in the organ, allowing you to have several different sounds available simply by changing manuals while playing, without having to change stops. You might want to practise by playing a chord on one manual and then moving it to another manual and playing the same notes. Try to do it quickly yet smoothly, so there is a minimal break where you lift your hand.