I would like to ask, how to connect Postgres to VB.Net ...?
The same way that you connect to any other database: using ADO.NET. This is one of the first places to look:
ConnectionStrings.com - Forgot that connection string? Get it here!
It will tell you what providers, standard and otherwise, are available for any particular database. You'll pretty much always be able to use OleDb and Odbc, which will require you to install an appropriate OLE DB provider or ODBC driver. There may also be a database-specific provider available, either from the database vendor or a third-party. Those may be free or they may not. Once you've picked an ADO.NET provider, the code pattern is exactly the same regardless. Only the specific types will change.
postgres .net - Google Search
Top answer = a .net native driver written by postgres team
Next answer = an article discussing connecting to postgres with ODBC
Native is preferred, but either would work