Originally posted by Opacho

Yes and no. the melody you come up with is usually the one played with your right hand (not in songs, but in piano covers, songwriters tend to write the melody down in notes for both hands) on the piano, what you need to support that is what you do with your left hand (chords or runs). You have to be able to provide both of those if you want it to sound exactly how you imagined it, otherwise the person playing the piano and writing the melody can improvise and 'figure out' what would work best for your base but that's honestly what makes the song and it may not necessarily be what you had in mind. Chord progression. I hope that makes sense.