If you are just starting with Selenium automation testing of your product, the first page you would probably want to automate would be the Sign Up or Login Page. If you have an online platform, like an ecommerce company or a Software-as-a-Service product, the Sign Up page acts as the door to welcome visitors to your web application.
It is one of the simplest yet one of the most important pages of your platform, and comes at the start of every possible user journey that you may want to test. Hence, it is also one of the most important web pages for your web application.