IO.puts

You're seeing just the function puts, go back to IO module for more information.
Link to this function

puts(device \\ :stdio, item)

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Specs

puts(device(), chardata() | String.Chars.t()) :: :ok

Writes item to the given device, similar to write/2, but adds a newline at the end.

By default, the device is the standard output. It returns :ok if it succeeds.

Examples

IO.puts("Hello World!")
#=> Hello World!

IO.puts(:stderr, "error")
#=> error