more on "!":

Run the given cmd/pipeline, and put it's output at the current cursor location:

    :r ! <cmd>

Filter the whole buffer through the given cmd/pipeline:

    :%! <cmd>

Filter a visual selection through the given cmd/pipeline: make selection (with mouse if you have :set mouse=a or gvim, or with any of the variations on 'v'), then hit '!'

you will pop into a command line like this:

    :'<,'>! <cmd>

'< is the beginning of the visual selection, and '> is the end.