texts in vendors

In transaction XK01 - Create vendor, where do we maintain the free texts

I used the "Extras--> Texts" option in Menu bar and then tried to extract it using READ_TEXT function module. but it is not extracting any data. Is there any other means of maintaining texts.

Esp I want to know how we come to know which text-id a particular texts belongs.

I have text-id Z003 but that has been given in the requirements only.

How will i come to know to which text type does it belongs to

eg: Z002 is for Invoices texts etc. ?

Please provide suitable solutions