Indentation without tabs

Question

What is the difference between indent-tabs-mode and tab-always-indent?

Answer 1

You can read the help for any variable by typing C-h v which runs the command describe-function.

tab-always-indent adjusts the behavior of the TAB key. As the documentation says:

Controls the operation of the TAB key.

If t, hitting TAB always just indents the current line.
If nil, hitting TAB indents the current line if point is at the left margin
or in the line's indentation, otherwise it inserts a "real" TAB character.
If complete, TAB first tries to indent the current line, and if the line
was already indented, then try to complete the thing at point.

Meanwhile indent-tabs-mode controls what character(s) to insert into the file when indenting a line:

Indentation can insert tabs if this is non-nil.

This is the most basic way you can choose between spaces or tabs for indentation.