Preeti,
Unless you add entries into your table how do you expect to see something?
The reason for you seeing some entries when you do a F4 is called as "search help". Basically when you perform F4, SAP will call a search help which is a snap shot of what values can be entered on the field.
In order to add entries into your table, you can:
1. Create a program and add entries into your Z table.
2. Create a maintenance view and then enter data thru SM30.
3. Mark the table with "display maintenance allowed" from the "delivery and maintenance tab" and then add entries using the menu path utilities->table contents->create entries.
Hope this helps.
Thanks,
Vikram.M