Ventura uses a web server as the middle-tier. Requests and responses go over the HTTP protocol.
Ventura's server runtimes are available for ASP.NET and ASP.NET Core.
See Choose between ASP.NET and ASP.NET Core on microsoft.com.
See topic Web servers for a brief overview of web server options.
To construct a middle-tier, you start by creating an ASP.NET or ASP.NET Core web application project in Visual Studio.
See Getting Started > Set up a Server project (middle-tier)
In its most simplest form the server only only needs 1 line of code. That would be setting the VenturaConfig.DefaultConnector to an AdoConnector containing the database connection string.