Here's a list to steps to connect to PostgreSQL in TDP
1. Install PostgreSQL ODBC driver
2. Select postgreSQL in TDP connection manager
3. Click Data source button to invoke ODBC DSN and add new PostgreSQL connection
4. Add the login information again in TDP to connect.
In general, it follows the same steps to add an ODBC connection, you can find it in help file under topic "Create ODBC Connections". Here's also an old video showing you how to add generic ODBC connection.
http://www.toadworld.com/products/toad-data-point/m/media-library/1108
Please let us know if you run into any issues.
Thanks!