Simply speaking, tempo is paces such as Marathon pace, half marathon pace and true tempo pace(5secs slower than HMP although different people have different ideas). You'd tend to run at these paces continuously, anywhere from 4 to 10miles.
Intervals are the recoveries in between the shorter faster reps at 10k pace and below. So you'd have sessions like for eg, 10x400 at 5k pace, off 60secs.
Classic week lay out, would be to have 1 session a week of either, and the rest of your running at easy pace.