Docker uses containers in packing and shipping the code, libraries and its other dependencies to make that application work in another computing environment also.
Docker makes the developers and operations guy work easy. Whenever a developer sents an application or software to operations guy for testing. For testing, The operations guy has to use the programming language of the same version, the same libraries in a particular OS which the developer used. Instead of this, DevOps can use Docker to pack the code and its dependencies to send Operations team.
In case you are interested to learn more about Docker, I would suggest you enroll in this Docker Training Course.
You can watch this video to learn more about Docker in DevOps: