Foo user = new Foo();.norm will use type infomation or attributes to map your class to a table exactly the same way I previously documented.
user.FirstName = "Jay";
user.lastName = "Fields";
user.ID = 0;
ConnectionInfo info = new ConnectionInfo("data_source","my_catalog","user_name","password");
DataGateway gateway = new DataGateway(info);
WhereBuilder where = new WhereBuilder("ID",user.ID);
The Update method takes an object and a WhereBuilder instance. The object is the object who's data will be used to update the database. The WhereBuilder instance is used to limit which records are updated. In the example above, only the rows in the database where the ID column is equal to 0 (the user.ID) will be updated. WhereBuilder has an And method that allows you to chain multiple equality tests.