How do you show to hold down a note, say a whole note, and play 4quarter notes at the same time?

hi - new here.. help appreciated.
Two variations of this question:
A)Whole note same as the first quarter note. B) And whole note different from first quarter note.
I can see stuff in the hand book under shared noteheads but whilst it shows an offset notehead it doesn't actually say how you create it. When I've tried to just edit or place the first note to a whole of 4 quarters it just deletes the subsequent quarters.
I'm new with musescore so instruction-for-dummies would be good. Help appreciated.