There a various skipper jobs and at the beginning you need to go through the same basic training but later you need to specialize for one area that are the most competent.
So in the beginning as I have already mentioned you need to pass basic course for controlling boats. This license gives you permission to control boats till 25 meters. However most of the skippers do later also specialization for various jobs that they will work at. You can specialize to sailing skipper, yacht skipper or powerboat skipper.
Person who will like to control powerboat needs to control boat at high speeds where there are just a few milliseconds to act and do what is wrong. There is not any time for errors and errors could be fatal. Powerboat skipper is person who usually drive also racing boats and have a lot experience. There knowledge is not just "push the throttle to the metal" but also in what kind of conditions you can go faster and in what conditions you need to slow down.
Usually those skippers have some other sailors that help them out with controlling big yachts. That kind of skippers are specialized in maneuvering big yachts, doing leisure yacht trips or sometimes a bit faster with a giant yachts that are not usually as maneuverable as you would thought. Yacht Skipper does the most work during the anchoring or getting in or out the marina, otherwise the riding with yacht is much easy to do.
If you are sailing skipper you need to have a deeper knowledge of winds and how does the wind affect sailboat. Sailing skipper jobs is the most difficult when you are by yourself with lifting sails and tighten them up for the best positions while you are controlling the sailboat and checking that the wind is and how will it change. It is job that you can not predict the situation of the wind and you have to be on a constant watch. There are a few signs to see if there are refills of wind, but more of that in later chapters.
All of Skippers need to have a good basic knowledge of lights on boat, engines, ties and especially navigation if all modern devices broke down.