Does anyone know how this can be done?

I wrote a session to maintain a new table I have created. One of the
table fields is a text. When the user enters and saves the text, I also
want to attach some keywords to text. How can I do that?

You need to write your default text in a file and then should set your default text group and use this function -

text.write() (http://www.baanboard.com/programmers_manual_baanerp_help_functions_text_fields_text_write)

What you are looking for are the predefined variables:

string attr.textkw1$(17) to attr.textkw4$(17)

Fill these up before you save your record.