The bash and shell relationships of Linux

Shell Popular Understanding: Translate user-entered commands to the operating system.

The

Shell is an interactive command interpreter. The shell is independent of the operating system, which gives the user the flexibility to choose the right shell for them. The shell lets you type commands at the command line, which is interpreted by the shell and routed to the operating system (kernel) for execution. The
    Shell is a command processor-a program that reads in and interprets the commands you enter. In addition to being a command interrupt, the shell is a programming language. You can write programs that the shell can interpret (known as source programs), which can contain shell programming commands and so on. In addition to explaining commands, the shell has other tasks, which can also be configured and programmed.    
    Shell has its own language that allows users to write programs and run in a complex way. The Shell programming language has many common programming language features, such as looping and control structures. Users can generate shell programs that are as complex as other applications.
The following is a summary of the shell functionality:
Find the location of the command and execute the associated program,
assign a new value to the shell variable,
perform the command substitution,
handle I/O redirection and pipeline functionality,
provides an explanatory programming language interface, Includes statements such as tests, branches, and loops.

    bash is the abbreviation for borne again shell, which is a kind of shell, A bash is used by default on Linux.
    When you enter a bash command on the command line, it's the equivalent of going into a bash environment, and if it's a bash environment, it's going into a child bash environment (equivalent to having a subprocess).