First of all, you need to make sure that the valve is closed before using the stem. This can be achieved by rotating the valve handle or using other controls. Ensure that the valve is closed to prevent fluid leakage or unnecessary flow.

Next, insert the stem into the stem hole of the valve. Stem holes are usually located in the center of the valve and are used to control the opening and closing of the valve. When inserting the stem, make sure it aligns with the valve hole and rotates freely.

Then, control the opening and closing of the valve by rotating the stem. Rotating the stem can change the position of the disc inside the valve, thus controlling the flow of the fluid. In general, rotating the stem clockwise opens the valve and counterclockwise closes the valve. Depending on the type of valve, the angle and strength of rotating the stem may vary.