Hi Karthick
I'm not sure what exactly do you need but in the first place you should open (to edit) any atom and locate button (third from left side) which, after clicking it, will open a new window with documentation about using variables. Or you can log in to B1iF, open new tab in your browser and use this link:
I guess all you need to know about variables is there. Check especially 3.3.7.3 section.
Kind regards,
Radek