Recognizing intervals
Link each interval to the opening of a song you know: the perfect fourth opens many anthems and marches, the perfect fifth sounds hollow and stable, the octave gives the same note twice. Sing the interval before answering: your voice helps your ear a lot.
In harmonic mode, both notes sound together: it is harder, but it is how you hear chords.
Major, minor, seventh
A major chord sounds bright, a minor chord darker; a diminished chord feels tense and an augmented one unresolved. Seventh chords add colour: the dominant seventh wants to resolve, the major seventh sounds soft and jazzy.