Explain what is Docker compose and what is it used for

Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services. Then, with a single command, you create and start all the services from your configuration.

For example, you can use it to set up ELK stack where the services are: elasticsearch, logstash and kibana. Each running in its own container.

In general, it's useful for running applications which composed out of several different services. It let's you manage it as one deployed app, instead of different multiple separate services.