LSP-format.nvim is a wrapper around Neovims native LSP formatting.

It does

1. Asynchronous or synchronous formatting on save
2. Sequential formatting with all attached LSP servers
3. Add commands for disabling formatting (globally or per filetype)
4. Make it easier to send format options to the LSP
5. Allow you to exclude specific LSP servers from formatting.

It does not

1. Provide any formatting by itself. You still need to use an LSP server

LSP-format requires Neovim 0.7 or newer.

Use your favourite plugin manager to install.

wbthomason/packer.nvim

-- init.lua
require("packer").startup(function()
    use "lukas-reineke/lsp-format.nvim"
end)

junegunn/vim-plug

" init.vim
call plug#begin('~/.vim/plugged')
Plug 'lukas-reineke/lsp-format.nvim'
call plug#end()

To use LSP-format, you have to run the setup function, and pass the on_attach function to each LSP that should use it.

require("lsp-format").setup {}
require("lspconfig").gopls.setup { on_attach = require("lsp-format").on_attach }

or

require("lsp-format").setup {}

local on_attach = function(client, bufnr)
    require("lsp-format").on_attach(client, bufnr)

    -- ... custom code ...
end
require("lspconfig").gopls.setup { on_attach = on_attach }

That's it, saving a buffer will format it now.

There are a couple special format options that LSP-format uses.

exclude is a table of LSP servers that should not format the buffer.

Alternatively, you can also just not call on_attach for the clients you don't want to use for formatting.

order is a table that determines the order formatting is requested from the LSP server.

sync turns on synchronous formatting. The editor will block until the formatting is done.

force will write the format result to the buffer, even if the buffer changed after the format request started.

You don't want to run formatting twice. If you had setup formatting on save before, remove it.
You can check if something is listening on buffer write events with :autocmd BufWritePre and :autocmd BufWritePost

Because default formatting is async, you can't save and quit in the same command. The formatting results will not get back in time and Neovim will close without applying the changes.
In this case you need to use the sync format option.

Add this abbreviation into your dotfiles to do the right thing when doing :wq

vim.cmd [[cabbrev wq execute "Format sync" <bar> wq]]

The main difference is that LSP-format.nvim is async by default. It will format on save, without blocking the editor.
When the formatting is done, LSP-format.nvim will only change the buffer if it didn't change since the time formatting was called.
And it adds some convenience with disable commands and format options.
But the end result is the same.

You can pass the format options into the setup function, or as arguments to the :Format command.
How the format options look like depends on the LSP server you are using.

The format options can either be string, number, boolean, or a function that resolves to those.

As an example, mattn/efm-langserver uses ${} template syntax with which you can define your own options ${--flag:lua_variable_name}.

require("lsp-format").setup {
    typescript = {
        tab_width = function()
            return vim.opt.shiftwidth:get()
        end,
    },
    yaml = { tab_width = 2 },
}
local prettier = {
    formatCommand = [[prettier --stdin-filepath ${INPUT} ${--tab-width:tab_width}]],
    formatStdin = true,
}
require("lspconfig").efm.setup {
    on_attach = require("lsp-format").on_attach,
    init_options = { documentFormatting = true },
    settings = {
        languages = {
            typescript = { prettier },
            yaml = { prettier },
        },
    },
}

Now Typescript gets formatted with what shiftwidth is set to, and YAML with 2 spaces by default.
And you can run :Format tab_width=8 to overwrite the setting and format with 8 spaces.