user_controller.ex

#...
def create(conn, %{"user" => user_params}) do
  changeset = User.changeset(%User{}, user_params)

  case Repo.insert(changeset) do
    {:ok, _user} ->
      conn
      |> put_flash(:info, "User created successfully.")
      |> redirect(to: user_path(conn, :index))
    {:error, changeset} ->
      render(conn, "new.html", changeset: changeset)
  end
end
#...