On a "normal" keyboard the NUM key is sued to toggle the numeric pad which
is usually found on the right side of the keyboard. In NUM mode it acts as a
numeric/calculator/telephone number pad. in non-NUM mode it becomes a
navigation aide.
By switching your laptop to NUM mode a series of keys (usually some of the
letters) become your number pad. The characters on these keys might be in
different colours, maybe white for letters and blue for numbers.
This is really a question you should now address to your laptop's manual to
discover how its keyboard operates. When you have learnt that, you can apply
it to programs that make use of these facilities, such as Excel.