Two Lines On One Stave (Piano Right Hand)

Trying to input a piano part and in the right hand there are 2 lines on one stave. One is semibreve chords and the other is a melody every time I try and add the second line over the top it keeps changing the values on the chords. Can someone tell me is it possible to enter these on one stave and if so how or does it have so have 2 separate lines created?