Or look for the DVD player on a disk that came with the laptop. They almost always bundle one.
The long answer to the question that you asked is that the DVD player only reads bits from the disk and presents them to the operating system. You need software that can decode the data, make it into pictures and sound, and present it to you. The decoding part is protected by licensing, copyright laws, and the You Can't Read Your Own Data Act (actually the Digital Millennium Copyright Act), so you need properly licensed software to play the movie that you own on the hardware that you own.