Many beginner writers often ask whether a plot outline is necessary.
The answer is, as it almost always is, that depends.
Some writers work better with an outline, some don't. You have to find out which of the two types of writers you are. Chances are that your personality would carry through to your writing process. If you're organized and meticulous in other aspects of your life you would probably need an outline, maybe even a very detailed one. If you are not that organize, maybe an outline is not for you.
Regardless, it's a good idea to know where you're going. If writing an outline, even a short point-form one seems like too much, then at the very least you must have a full idea. Otherwise, there is a good chance you won't be finishing what you started.
A full idea means not only something vague, but an idea that is developed, at least partially, and that you know what you want to do with it and where you want to take it. Endings are otherwise very tough.
So guess what. To find out what kind of writer you are you know what you're going to need to do. That's right. Write.