On a sunny day, what do we use to tell the direction at night?

If it is sunny at night, of course, it is positioned with the Big Dipper.

Find the "spoon" in the sky, that is, the North Pole constellation. Take the zenith star along the outer edge of the spoon mouth as the standard, and take the distance from the top to the bottom as the unit length. There are seven less bright stars along the extension line, that is, the Polaris, that is, your position is due north.