What does build command do?

The build command is used to build an image from a Dockerfile, but the command has to be run in the same directory as the Dockerfile. When an image is built, the commands specified in the Dockerfile are executed. The operating system is installed​ along with all the packages required in the Docker container.

What is build essential Linux?

What is build-essential? The build-essentials package is a reference for all the packages needed to compile a Debian package. It generally includes the GCC/g++ compilers and libraries and some other utilities. So if you need to install C/C++ compiler, you just need to install build-essential package on your machine.