Donate button with easy JS include in website?

[PKiula]

Hello. We'd like to enable a DONATE button on our website, which should bring up a simple credit card form... and when user submits, basically make the payment into our account. 

We use wordpress for our website, but this is not really wordpress. I should be able to do this with a simple static website, just with a "widget" style JS include that includes error states etc within the widget if a user enters the wrong credit card info and such.  

Where can I find help on this simple stuff?

1. I create a Square Online account for this? Like a merchant account on Paypal?

2. Then what.. where's the JS include? 

Our website is in PHP, but I can include JS anywhere. 

Many thanks for any pointers!