Keywords are the words people type into a search box when they are looking for information or something to buy. You want to use these words in your posts and advertisements so that these people will find you. Profitable keywords are the ones buyers are using.
Now, how can you find these words? This video suggests some very simple ways and also some more complex and expensive methods. So if you want a page one Google ranking and lots of buyers coming to your website use your targeted keywords a lot. Few people look beyond the first page of Google so you want to be there.