I created an account there now I need to know how I can the link to the button 

 This may have the answer:
 https://developer.calendly.com/how-to-display-the-scheduling-page-for-users-of-your-app 

 That depends on how your webpage was made. If you don’t know, then you probably have to contact the person that made the webpage for you.  

 https://www.appointlet.com/ is a better alternative to Calendly. The free version has more features than the free Calendly and the paid version is also cheaper.