Vis uses lua for scripting and thus configuration, at startup a file called visrc.lua is loaded, this must reside in any of its configuration directories (See FILES section in manpage).

The file location usually is $HOME/.config/vis/visrc.lua

If you are unsure where it is located launch vis and run

:help Lua paths

A default visrc.lua is offered in your vis installation directory, copy it to your $HOME

this should be either /usr/local/share/vis or /usr/share/vis (or wherever you found it in :help)

mkdir ~/.config/vis
cp /usr/local/share/vis/visrc.lua $HOME/.config/vis/visrc.lua

The file contents are explanatory

-- load standard vis module, providing parts of the Lua API, sets _G.vis
require('vis')

vis.events.subscribe(vis.events.INIT, function()
	-- Your global configuration options
end)

vis.events.subscribe(vis.events.WIN_OPEN, function(win)
	-- Your per window configuration options e.g.
	-- vis:command('set number')
end)

For further information see the lua api

It is recommended that you install and add vis-plug to your visrc.lua, See Plugins.