How to compose using a coding form created in Wix code for an external mailing system
Do you mean like using SendGrid as the external mailing system? There is a sample on that if you just search Wix site or click here for the simple sample.
But I want to do it in another system Is there a tutorial on how to connect systems and forms in the wix code
I want to connect this system to a form in Wix code:
If you want to di it an external system that is not present in any sample of that Zapier can connect to you will need to create your own integration. Probably reading about Wix Fetch is a good starting point but it will require some coding to accomplish this.
You can refer me to the page Let's have an explanation of this in Wix
You should start with Wix help documents and go from there to the wix Code API.