The standard definition of an enzyme is a protein molecule that functions as a biological catalyst, allowing reactions to occur more quickly than they normally would. The reason enzymes are able to do this is because they lower the activation energy of the reaction, making it more energetically favorable for it to occur. Enzymes are able to lower activation energy and speed up reactions in four ways.
The first of which is simply by placing substrates in contact with one another in such a way that the necessary catalytic groups can then interact. Secondly, enzymes bind and place substrates in a specific orientation that causes the substrates and catalytic groups to be located in proximity to one another, leading to a decrease in the amount of energy needed for the substrate and catalytic group to interact. Thirdly, enzymes may provide charged side groups in their amino acid structure that can help to stabilize transition states between the initial product and the final product of the reaction being catalyzed. Fourthly, enzymes are able to decrease the naturally inherent motion of substrates and their catalytic groups by essentially locking them in place.
It is through these four processes that enzymes are able to speed up the rate of chemical reactions by lowering the activation energy required for the reaction to occur. Hope this helps!