Hi there

I am completely new to Salesforce, and I apologize in advance if this question has been answered before. 

Basically, a Client has all their customer details in Salesforce, and has been sending out Emails via it as well as keeping track of all their details through there. In short, we have developed a website for their customers to go to, and they update some options and it saves to a SQL database on our server. This all is completely separate to Salesforce. 

What we wish to achieve, is that once this page has been filled out, that we can set a particular field inside Salesforce which corresponds to that users Email, or name, or Id. So basically, once the page is done, they click “Finish” on the website, it runs a function which sets a value in Salesforce to “True”, for example, against their contact details. Is it possible to get these two to talk together, and if so – where do I start? 

Thanks for any help you can give!