Normally you will create the percussion in the beat-&-bass editor and the melodies are created in piano-roll as midiclips that will be placed in song-editor together with the references to the percussion (as clolor-bars) and that will be your song.
I believe this link will be of value for you:
http://lmms.sourceforge.net/wiki/index. ... _with_LMMS
The images are not updated but the text is pretty much valid.
If you have other problems -just ask -seeking information is not stupid at all.
Br.