>>>whether you will need to have several windows open at once.
Well even the worst CPU going will let you have several Windows open at once so that is hardly a good measure.
The B950 is an entry level "value" CPU. So it is not the worst you could get, but it is a long way off being the best you could get.
If all you plan to do is email, internet and office work it will be fine.
But dont expect to play any powerful games on it.
If possible try to get an Intel i3 CPU which may cost you a little more but is an all round better CPU.