Emacs

open
emacs& RET     or click a graphical icon
emacs -nw RET     start in terminal, not in a windowing system

cancel

C-g     a command

M-g g    Go to line #

Text size
Shrink/Grow: C - - / C - + 

Copy & Paste

C-<space>
    Start selection
C-w
    Cut
M-w
    Copy
C-y
    Paste

12.1.2 Killing by Lines

C-k

Kill rest of line or one or more lines (kill-line).

C-S-backspace

Kill an entire line at once (kill-whole-line)

M-: evaluate function in minibuffer

(vi yy): C-a (beginning) C-spc (highlight) C-e (end) C-y (yank)

M-<Move to the top of the buffer (beginning-of-buffer). With numeric argument n, move to n/10 of the way from the top.
M->Move to the end of the buffer (end-of-buffer). 

15.10.4 Query Replace

M-% string <RET> newstring <RET>

Replace some occurrences of string with newstring. 

C-M-% regexp <RET> newstring <RET>

Replace some matches for regexp with newstring.

26.3.2 Indenting Several Lines

C-M-q

Reindent all the lines within one parenthetical grouping. 

C-u <TAB>

Shift an entire parenthetical grouping rigidly sideways so that its first line is properly indented. 

M-x indent-code-rigidly

Shift all the lines in the region rigidly sideways, but do not alter lines that start inside comments and strings.

C-u 4 M-x indent-rigidly to indent the region by four spaces, C-u -4 M-x indent-rigidly to remove four spaces

Also, in Python mode, with a marked region, use C-c > and C-c <

Displaying in Another Window

C-x 4 is a prefix key for commands that select another window (splitting the window if there is only one) and select a buffer in that window. Different C-x 4commands have different ways of finding the buffer to select.

C-x 4 b bufname RET

Select buffer bufname in another window. This runs switch-to-buffer-other-window.

C-x 4 f filename RET

Visit file filename and select its buffer in another window. This runs find-file-other-window. See section Visiting Files.

C-x 4 d directory RET

Select a Dired buffer for directory directory in another window. This runs dired-other-window. See section Dired, the Directory Editor.

C-x 4 m

Start composing a mail message in another window. This runs mail-other-window, and its same-window version is C-x m (see section Sending Mail).

C-x 4 .

Find a tag in the current tag table in another window. This runs find-tag-other-window, the multiple-window variant of M-. (see section Tag Tables).

Deleting and Rearranging Windows

C-x 0

Get rid of the selected window (kill-window). That is a zero.

C-x 1

Get rid of all windows except the selected one (delete-other-windows).

C-x ^

Make the selected window taller, at the expense of the other(s) (enlarge-window).

C-x }

Widen the selected window (enlarge-window-horizontally).