A lot depends on what you are using to record/play the chords eg a midi keyboard and one of MMMs in built synthesizers, one of MMM synthesizers and the Midi Editor interface?
Have read the Midi Editor section of the installed pdf manual - see under Help in MMM
Trying to play chords is possible using the internal keyboard ie the computer keyboard however is can be difficult as the key/note combinations are not necessarily in the correct places more specifically a US keyboard has the | key in a different position. MMM is set for an International keyboard layout as shown in the image
So the key sequence | Z X C V B plays the notes C D E F G A
With a US keyboard the | key is in a different position.
If this is a one off project try using the Midi Editor where you 'draw' the notes and can set up your chords etc - however I find this is very time consuming the manual gives you more information on using this.
The best way, if possible, is to use a USB Midi keyboard, so you can play the chords directly using your selected synthesizer in MMM, again see the manual about using an external keyboard.