Songtrix

To import a melody from a midi file, use File-Import Midi and follow the options to bring the melody (and other tracks if any) into Songtrix.

To import a melody from a midi keyboard, use Segment-Record.

Once the melody is there, you need to add the chords you want to use.  If you need help with these, you might find it helpful to select areas of the song and use Notes To Chords.  You will need to use your own musical ability to choose the best chords.

Once the chords and melody are there, select all other tracks and turn all segments into autostyle segments (Segment-Autostyle).

Then select a style from the dropdown list on the Transport Bar.  Change styles to experiment with the effects.