soft ways

I am going to create a saas product a screenshot sharing website. I have seen late of people talking about product validation a landing page and get pre order before even creating an actual product. I want to know what should include in this landing page? and is it really possible people will do a pre order for a screenshot / image sharing product ?

Hi, I am a developer of 2 years of experience. I want to build saas product. What i have no clue where to start and how to find good idea. I my thinking about an copy idea an run it. Like copy this https://snipboard.io/ and ad some new future and test. Please let me know if i am right or wrong.