To set up indentation configuration you have to decide its size and if you want to use spaces or tabs for it. Vem, by default, uses 4 spaces to indent text and code.
There are four main options to control indentation:
tabstop is the size of a tab character in the file.
shiftwidth is the indentation size that will be used when indenting blocks of text and for automatic indentation.
softtabstop is the indentation size when you press the tab key.
expandtabs is the option to indicate if you want to use tabs or spaces.
You can combine these options in various forms to create very peculiar setups, but most of the time you may want to set an unique indentation size and choose between spaces and tabs:
To use spaces:
set expandtab set softtabstop=<size> set shiftwidth=<size>
To use tabs:
set noexpandtab set tabstop=<size> set softtabstop=<size> set shiftwidth=<size>
Replace <size> by the amount of characters you want to use to indent.
Note that setting this options don't change the preexisting indentation format of a file. If you want to change how a file is indented (from tabs to spaces or the other way around), check the :retab command.
Sometimes you may want to set the type/size of indentation according to the file type that you are editing. For example, you could need to use tabs of size 8 in C source code files but 2 spaces in HTML files. To do something like this, check Configuration per filetype.