This depends on the type of manual juicer you use.
Handheld juicers rely on the user using their strength to squeeze the fruit. Place the fruit between the two arms, and squeeze with your hand to extract the juice. If you’re using a jug reamer, you’ll cut the fruit in half first (usually a citrus fruit), and press it down onto a ridged cone.
Hand presses and crank-operated juicers work with machinery that springs to life once you turn the crank or pull down the lever.