A network protocol is an established set of rules that determine how data is transmitted between different devices in the same network. Essentially, it allows connected devices to communicate with each other, regardless of any differences in their internal processes, structure or design. Network protocols are the reason you can easily communicate with people all over the world, and thus play a critical role in modern digital communications.
As a DevOps engineer you will need to understand the basics of networking protocols, how they work, and how they are used in the real world. To get you started, you should learn about, [TCP/IP](https://en.wikipedia.org/wiki/Internet_protocol_suite), [HTTP](https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol), [HTTPS](https://en.wikipedia.org/wiki/HTTPS), [FTP](https://en.wikipedia.org/wiki/File_Transfer_Protocol), [SSH](https://en.wikipedia.org/wiki/Secure_Shell), [SMTP](https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol), [DNS](https://en.wikipedia.org/wiki/Domain_Name_System), [DHCP](https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol), [NTP](https://en.wikipedia.org/wiki/Network_Time_Protocol).
Here are some of the resources to learn about SSH:
Docker is a platform for working with containerized applications. Among its features are a daemon and client for managing and interacting with containers, registries for storing images, and a desktop application to package all these features together.