When you have first created a Table, it is recommended that you enter at least a couple of records of data into it.
This is so that as the design progresses, and you create Queries, and embed them onto pages, there is some output to see. Otherwise you will be effectively designing 'blind'.
If you will be using the default data entry screen provided by the Table, you could even enter all the data for the Table at this time. If you plan to design a custom data entry screen, you should leave some records for entering later to test that screen.
It is sensible to use real data wherever possible, rather than nonsense dummy or 'greeked' text. This is because in a complex site it can be easy to overlook the dummy data when the site later goes live, and embarrassment may ensue.