Info

Info' is the Help browser in GNU Emacs. Think F1.

M-x info-apropos

Don't know where to go. Try this command. For example, try M-x info-apropos RET compile RET to see some idea of what you can do.

[C-h r] (or M-x info-emacs-manual)

Learn how to use GNU Emacs

[C-h i] (or M-x info)

See what manuals of all packages that come with your GNU Emacs

[i]

While in an info buffer, jump to some topic of interest. To learn about regular expressions try [C-h r] and {{Keys|i regular TAB}.

[I]

Same as [i] but gives you a list of links.