Connect the positive terminal of the battery with one electrical contact of your light bulb and the negative terminal with the other electrical contact of the bulb. Many bulbs have one electrical contact with screw threads on it, with the other contact as a round dot on the end of the base. Other bulbs will have metal prongs sticking out. Use a bulb which matches what your battery can put out. If the battery has too low a voltage, the current flowing through the bulb will be small and the bulb’s filament won’t get hot enough to visibly glow. If the battery has too high a voltage, so much current will flow that the filament will get too hot and vaporize. Flashlight bulbs work with about 3V, easy to obtain with two batteries in series.