Hey there, @CoachMaria - thanks for your topic! Firstly, check out our New User Guide - it’ll def prove helpful as you get used to the platform!

This Calendly user has selected an embed to use on their website (using “preview availability” as the text in the widget) and made some adjustments (which you might need the help of a developer to do if you are not a developer yourself)! Check out this handy overview of our embed options! You can also take a look at this website for examples of each one.

Just taking a quick look, I think what they're doing is using our embed's notifications to the parent window to listen for when when someone has selected the date and time, and deleting the embed element from the page and displaying their custom message instead. However, I cannot tell you exactly what this Calendly user has done on their website or exactly how to achieve it, since what they did involves developer tools that they have customized for their own use case. 

If you are looking to do custom development on your web page, we do suggest getting the help of a developer. This is a great place to tell them to reference to get started. Good luck! 

P.s. I have moved your question to our Developer Q&A and did get the help of a developer support specialist to answer your question. If you have further questions, I will make sure someone chimes in to at least direct you correctly! =)