1. By running external table mapping, we need to select database name and table. Pega will create class, properties (same as the columns presented in the database table), pega class to database table mapping(in class rule) and data base table mapping with an external database table.
For Example, if you have a external data base called Customer Data and table name as LoginDetails, which has all the customer details with columns such as First Name, Lat Name, DOJ, AccessNo...
If you run New External Database Mapping wizard, you need to provide the database name and table name. Based on this pega will show you the appropriate class name, properties which are going to be mapped to that class. All these properties are going to be created in the newly created class with the same name as column.
We can override these properties if we want.
2. Connector and Metadata Wizard, basically used to create any integration related connectors. For example, If you want to fetch weather report(For this we wil get WSDL file from internet). In this we need to upload the WSDL file and pega will create the related rules such as connector rule, class rule, XML rule, Parse XML, which are required to run the weather report service from pega end.
Both the External Database Table Class Mapping wizard and the Connector and Metadata wizard create a database table, classes, properties records for you.
The main difference between these two wizard as per my observation is that we cannot map Pega OOTB tables like pc_work(whose primary key starts with px,py,pz) using Connector and Metadata Wizard but that can be possible with External Database Table Class Mapping wizard.