The way of Emacs

Question 1

Negative Universal Argument

Answer 1

C-- or M--

Before any command, when M-d will kill next word, M-- M-d will kill previous

Question 2

Help during prefix commands

Answer 2

For commands “grouped” together by common prefix (like special characters under C-x 8 ...) you can find all possible “endings” with C-h (C-x 8 C-h)

Question 3

Apropos

Answer 3

C-h a apropos-command .
and slightly more general apropos which will also search through functions and variables.
Will perform a general search for keywords in commands and its documentation.

Question 4

Function description

Answer 4

‘C-h f` will show docs generated from code comments.

C-h F will try to show full documentation (in plain English).

Question 5

Find key bindings.

Answer 5

C-h w where-is.

Will display key bindings to given command.

Question 6

Find command under some keys.

Answer 6

C-h c describe-key-briefly just in minibuffer.
C-h k describe-key for “full” documentation.
Could be used if you would like to modify or learn more about often used key binding. To learn more just C-h k C-h k.

Question 7

View messages.

Answer 7

C-h e will display message buffer. Also accessible as any other buffer C-x b *mess...