It is best to use a GPU when playing a game or doing video editing. However, integrated graphics on your CPU will still work in a pinch.

While testing Halo Wars Definitive Edition on my Surface Book, I noticed that it wasn't using the powerful discrete NVIDIA GPU, defaulting instead to the integrated graphics.

If your PC is using integrated graphics instead of GPU, first of all, check all your cables, force programs to use dedicated GPU, and check this post.