Width
To make indentations 4 spaces wide:
:set shiftwidth=4
Spaces
To use spaces as indents, 4 spaces wide:
:set expandtab
:set softtabstop=4
softtabstop and sts are equivalent:
:set sts=4
Tabs
To use tabs as indents, 4 spaces wide:
:set noexpandtab
:set tabstop=4
tabstop and ts...