What is the function of biochemical enzymes?

Biochemical reactions, in simple terms, are the chemical reactions that take place inside cells, that is (we can also say) living organisms. These reactions are the key to the maintenance and propagation of life. However, like many other chemical reactions, these reactions are also very slow and will take a long time to complete, unless they are catalyzed by catalysts. A catalyst is a substance that speeds up the rate of a reaction or allows it to take place under a different set of conditions without being changed by the differences.
Enzymes are the catalysts in biochemical reactions. These are proteins that enable the biochemical reactions to complete at faster rates. Enzymes are able to do that because of their ability to reduce the activation energy of a given reaction. Enzymes can also allow the reaction to be completed through an alternate reaction pathway which has lower activation energy. In either case, the products of the reaction will be the same.
Interestingly, the enzymes are very specific to biochemical reactions, which means the same enzyme will not be able to catalyze any other reaction than a specific one. Also, an enzyme will be unchanged by the biochemical reaction it catalyzes.
In summary, enzymes catalyze biochemical reactions.
Hope this helps.