So in this picture you can see both tweets on the lower third of the females body. The pups do not latch on as her nipples are inverted. Think about dangling nipples in the sea....good things to nibble on by fishes, not fun. So it works like a pressure machine that stimulates her to express the milk.
you can see in this picture how much of an indent the pup makes in the blubber of mine to stimulate her to release the milk. with over 50% fat in her milk, the pup will gain upwards of 240 pounds to the 60 pounds birthweight. When he is weaned, he will look like a stuffed sausage. He will then just lay upon on the beach for several months. Gradually getting into the surf on calm days and learning to swim. He will go through his first catostraphic molt before he will head out to sea for good. He will only return for the birth season haul out, maybe a fall haul out and then more molting the next year.