How to add Google and Facebook login buttons to custom form with Velo

I can use Google’s APIs and do this but I’m not sure if I add my own codes for custom login with Google will it work for old users which already signed up with Google or Facebook? Or they will automatically create a brand new account.

Example: (I’m a member)
Let say I have already used Google sign-in buttons which are created by Wix. And I bought something from the store and when I use the same login details I can see my past orders.

And let say I did a form using Google’s APIs and created my own Google sign-in button. If an old user which already used Wix’s Google sign-in button, use my own Google sign-in button will the user see his past orders and other information? Or it will automatically create a new account for the same user.

Did anyone try to do this or any clear answers for it?

I will use: Google’s APIs or similar things to this I’m not sure if I found the right thing for me but I will use Facebook’s and Google’s APIs in order to do that.