One action is a cause, which leads to another action that is the effect of the first action.
A cause and effect relationship happens when an event causes other things to happen. Therefore, the event itself is the cause and everything after that event which is a direct result of it is considered the effect. For example, Romeo appearing at the Capulet's ball is the event that causes many other things to happen such as falling in love with Juliet and Tybalt's desire to seek him out for revenge.