How does Canon 760d shoot the starry sky? Why can't it focus?

First of all, you should prepare a tripod and wire control. Shoot on a clear night. It's best to adjust the aperture of the lens to the maximum to let more visible light in. It is not easy to focus at night, so focus manually with MF on the lens. I have an experience, generally manual diagonal, turn to the end, and then a little later, you can get it. Shutters usually take a long time. It is recommended to be around 8 seconds. Don't drive for 30 seconds, or longer, it will make the track of the stars look like a star track.