It's a wide field, let in mint that HW is modular like SW, but abstraction does not get too far, computers are really physical things, and (IMHO) left out VHDL FPGA and similar, they are not necessary at beginning, and transistors too, the base is digital logics, combinatory and sequential circuits, then look at a very simple CPU (8 bit), then a simple system (CPU + memory).

A good old book will help, (EG) look at: Digital Logic And Computer Design - Morris Mano (free pdf at archive.org)