i have to add some text at cursor point i n indesign

If there is no text highlighted (you just have the flashing 'cursor point' then that can be referenced as the selection..

app.selection[0].contents = "Welcome";

If your "cursor point" is a selected text insertion point or selected text then simply do:

app.selection[0].insertionPoints[-1].contents = "Welcome";

But maybe—I'm not sure about that—you want to load text to the placegun?

Then you could create a text document first and load that to your placegun.

Regards,
Uwe

var _text = 'Welcome!';
app.activeDocument.textFrames[0].insertionPoints[0].contents = _text;

Moved to the scripting forum....