You got a placement!
If this is the first time this has happened for you as a writer, you have just taken your writing career to a whole new level...congratulations! What a "placement" means is that someone (a TV or movie producer, a TV or movie music producer, etc.) has heard your song, thought it was perfect for their project and is going to use it in their movie, TV show, commercial, infomercial, or something else that you see everyday on the tube!
What do you do?
You don't have to do anything!.....EXCEPT tell us whether you approve or disapprove of the usage. If you should accept the usage, we will issue what is called a "sync license" which gives the user of the song the right to "sync" your music to their visual display.
Then you sit back, crack a cold Corona in your new Cadillac, and watch the royalties roll in (within about a year of the use's premier.)