Add a contact from a website

Hi guys 

I am trying to find a simple method of adding a user name and email into the list from a form on our website. I have tried using a sample code from Github . I am struggling to generate an access token first before I can use the app. 

Also, I don't even know if my developer account is automatically linked to my clients user list. How can one check this?

Please can someone help. 

Greg