Melody is the line you follow or sing. Accompaniment supports it with harmony, texture, and rhythm. Bass gives weight to the low register and helps define both the harmony and the groove.
These roles can overlap. A solo guitarist can suggest a bass line, chords, and a melody at once. A band can trade roles throughout a piece.
When improvising with others, leave room for them. A pause can be as expressive as a note, and matching the groove often matters more than adding complexity.
Pick up your guitar
Play an open low E as a simple drone. Explore E Dorian above it and listen to how the drone establishes the root.