The Weak force is responsible for what we call radioactive elements. The Weak force also allows the Sun to provide us energy. It allows one element to turn into another one. As its name implies, the weak force is kind of wimpy, but that is because it only happens at short distances. If you are far away from something, the Weak force won't affect you, so we only know about it at the subatomic scale. The Weak force is carried by W and Z bosons. The W bosons each have electric charge, but the Z boson has no electric charge. Neutrinos only interact via this force.

Learn about the Electromagnetic Force
Learn about the Strong Force