create more than "1 voice"

sorry, i' very amateur...im learning a lot, but i have a big problem building this figures, i put a little example
having a 4/4..

1- i put 2 white notes, "voice 1" -> it is ok

2-i put 4 black notes, "voice 2" ->it is ok

3-now, i want to put the 2 voices at same time in sheet, but musescore does not allow me...i know this is legal when building a sheet..but something im doing wrong
thaks my friends