You've provided no details about your computer, so I can't give a precise
answer to this, but have some suggestions:
Firstly please reply and post details of the make and model of the laptop
(at the very least).
Secondly , read the user manual for your laptop. If a copy didn't come with
the machine, then the manufacturer website would usually have a PDF copy
available.
Thirdly, at a very rough guess, I would say you need to press a combination
of the "Fn" key and one of the "F" keys (the ones number F1 - F12 like Fn+F5
or whatever). It could be any one of these 12 (or perhaps 10) "F" keys.
Each of these keys does something different, like turn volume up and down or
swaps between monitor and projector or external monitor etc.
Finally (and this is probably not an issue) if it's some sort of hardware
problem (microphone not working for some reason), you need to take the
computer back to the vendor from whom you purchased this (or their
authorised service agent) claim service for it (under the terms of the
warranty if necessary).
Also check that the hardware devices are all up to date with drivers and
software etc. (also usually available from the manufacturer's website).
