Parallel notes of different length

Hello:
I am trying to write notes for classical guitar. Doing so I did not find how to get a bar with a semibreve as base and four parallel quarter notes. - Parallel notes in musescore alwways seem to have the same length. - I read the tutorials carefully and I still have the feeling that there is just a little thing that I have not understood.
I'm grateful for your help!
Joh