How does catalyst increase the speed of reaction?

A catalyst lowers the activation energy of a chemical reaction . As a result, less energy is required to make the chemical reaction occur and the chemical reaction can occur more easily. So, the speed of the reaction gets increased. Note that some catalysts decrease the speed of the reaction instead of increasing it. In that case, instead of lowering the activation energy of the chemical reaction, they increase it and hence in that case the speed of reaction is decreased. Such catalysts are called negative catalysts. Note that activation energy of a chemical reaction is defined as the minimum amount of energy needed to make the reaction to occur.