class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception
end

<form action="/users" method="post" accept-charset="UTF-8">
<label for="username">Username:</label><br>
<input id="username" name="user[username]" type="text" /><br>
<label for="email">Email:</label><br>
<input id="email" name="user[email]" type="text" /><br>
<label for="password">Password:</label><br>
<input id="password" name="user[password]" type="text" /><br>
<input type="hidden" name="authenticity_token" value="form_authenticity_token %>">
<input type="submit" value="Submit">
</form>

Rails.application.routes.draw do

resources :users, only: [:new, :create]
end