Friend is a module… it should contains functions You can call.

In your code…

defmodule Friends do
    IO.puts "start"
    person = %Friends.Person{}
    Friends.Repo.insert(person)
    IO.puts "saved"
end

it could be

defmodule Friends do
  def save_a_new_person() do
    IO.puts "start"
    person = %Friends.Person{}
    Friends.Repo.insert(person)
    IO.puts "saved"
  end
end

And then You can call it like this

iex> Friends.save_a_new_person() 

Why would You expect your code in the module to run? or when?

As @kokolegorille has already pointed out, you shouldn’t run db commands outside of functions, since then they would be executed during compilation before the database connection process is started.

Put those commands in a function, and execute the function when you need to. It can be in response to a controller action or whatever else.

Also maybe read through the official elixir guide to get a better understanding of how elixir modules and functions work.