Can you pl. tell me how to differentiate when to use "using" or "by using"
Select Export using the Export dialog box
Select Export by using the export dialog box.
Those two examples say the same thing slightly differently. In this situation neither is more correct than the other. In the first one "by" is just implied.
You can think of them this way:
"Select Export using the Export dialog box." is like saying "When using the Export dialog box, select Export."
"Select Export by using the export dialog box." is like saying "Use the Export dialog box in order to select Export."
This is hard to explain because there is not a big difference. You can say it either way. Don't dwell on it, you'll understand it as you speak english more.