Material within angular brackets denote logical entities, e.g., <user> indicates that you should type your user-name. The shell's prompt is denoted with "$ ", so, e.g., the following indicates that you're supposed to type ls to the shell:
$ ls
Especially in the section about emacs key sequences are written with the convention that:
S- means hold down a shift key,
C- means hold down the control key,
M- means hold down the meta key. (This is the left Alt key).
RET means the return key. Certain other named keys are written with their names.
So, e.g., C-x C-f means holding down the control key and pressing "x" followed by "f".