Hi nitin_greg,
If you are able to uniquely identify the textbox element with the application modeller (if the text is changing time to time, you can use wildcards for the value attribute), you can use a navigate stage's click center action.
If you can't uniquely identify the element, you have to identify the window/webpage itself with win32 spy, then with a navigate stage's golobal mouse click action you can click on the desired X / Y coordinates.
I hope this helps.