Make love, making love, love-making.
(I will try and be as brief as possible.)
Make love: a poetic phrase expressing the act of sex. Due to it's romantic undertone, it's another way to say "have sex" without sounding..rude, I guess.
Making love: "We're making love tonight", "He was making love to the camera". The first way means to have sex, the second means to purposely seem photogenic.
Love-making: the noun that signifies having sex. Ex. "There's some love-making going on in that room."
Hope this helps.