Sometimes an editor, especially a newer one, is tempted to write an article about an idea that they or their friends have come up with, such as a new ball game, a new word or phrase, a film you uploaded to YouTube, or a new language. It's natural to want to tell the world, and Wikipedia seems like a great way to do that.
There are several things wrong with doing this:
Of course, everything in Wikipedia was made up or discovered by someone at some point in time, so how can your idea join them? Essentially, you have to persuade others that it's important first – and those people have to think it's sufficiently important to write book, newspaper or magazine articles, or academic papers about (not just mentioning) your idea. Such resources are considered reliable, and therefore the subject can become eligible for Wikipedia. It is important that someone else other than the originator of the idea do the writing, as notability can be conferred only through independent attention; see Wikipedia:Notability. Advice on how one can obtain this kind of independent attention is beyond the scope of Wikipedia, and as such, seeking notability lies in the hands of the individual.
As an example, consider the history of the game Scrabble. It was originally invented by Alfred Mosher Butts in 1938. At first he made only a few copies, to give or sell to his friends, and contacted several game manufacturers, all of whom turned him down. Therefore, had Wikipedia been around in 1938 it could not have had an article on Scrabble. Even though Butts had invented a game which would eventually become a worldwide bestseller, at the time it was known only to a few people, and little or nothing had been written about it. However, he was not disheartened and kept promoting his idea, until several years later it was bought by a games manufacturer, sold in many stores, and became widely known and widely written about. This is the point at which Wikipedia could have had an article about it, as opposed to when it was first invented.