What is Linux Shell ?
In the early days, computing instructions were in 0's and 1's. It is difficult for human to read and write. A special program call shell would accept the instructions in English and pass to kernel. Shell is a command language interpreter that executes commands from input device (keyboard or file or something else). Shell is not part of the kernel, but uses the system kernel to execute program, manage files etc.
Ch 1, 2, 3, 6 Getting Started, Utilities, vim Editor
Ch 4, 5 Filesystem, The Shell
Ch 8 Bourne Again Shell / BASH shell
Ch 10 Programming the Burne Again Shell