The Nobel Prize in Chemistry 2018 was given in two parts. The first half was given to Frances H. Arnold and the second half was shared by George P. Smith and Sir Gregory P. Winter. All these three scientists used controlled evolution to make chemicals that tremendously benefited humankind.
Enzymes are biological molecules that act like catalysts in biochemical reactions. That means they speed up reactions between other molecules but remain as it is at the end. For example when you go to the shopping mall, a woman working there can help you to quickly find something that you are looking for and buy it. Without her help you might take a long time. So the woman acts like a catalyst.
Now, not all these enzymes are very efficient. For example, there could be a fat and lazy boy who might take forever to walk you to the right aisle or a new girl who does not know where it is.
There is a biological process called natural evolution. Small and simple organisms have been continuously evolving to be bigger and more complex organisms. This happens at a molecular level by genetic mutation or change. You can think of a guy working at the mall for many years and getting very good at his job.
Now these three scientists used interesting engineering methods. They exploited evolution to make more efficient enzymes. They used random mutations to make different variations of the enzymes and selected the ones that performed better. This is a much faster method than natural evolution.
For example a new guy might take many months to learn about the products that he is in charge of. But if you can test the performances of 10 new candidates and select the best one maybe you can find somebody who worked in another mall before and already knows about some products. The ability to select saves you time and effort.
Then these scientists repeated the process. They took the best performing enzyme, made more variations of it and tested their performances. After a few rounds like this they finally got impressively efficient enzymes that increased the productivity tremendously.
The enzymes engineered by them were very useful in manufacturing many chemicals like renewable biofuels and medicine that were used to cure many diseases like cancer.