I had a Kawasaki Ninja that had "sticky" clutch plates that would happen after only a few day's sitting. One of the symptoms is that the bike won't roll with the clutch lever pulled in, like it stays in gear, another is that when you go to start it and the clutch lever is pulled in, the bike will lurch forward as if it is in gear. To free it up, squeeze the clutch lever and put the bike in neutral and get on it and roll it forward or in reverse a few inches and that will loosen up the plates. It may take a little effort at first, you are only overcoming the very thin layer (or no) oil between the clutch plates, just sort of gluing them together by the friction generated by their proximity to each other. There is no damage done, just moving them a little to get some more lubrication in there can fix it and then it will all be fine.
Like others have said, we need a little more info to tell where the oil is coming from. And, like TW-B said, are you sure it's oil, or are you leaking a little gas on the ground from the carb overflow because of a stuck, dirty float needle?