How does one use these noodle things? Do they wrap around the waist or what? I cant figure them out by the photos.
hmmm, like anna said, stuff them between patas and you are good to go

easy way: sit on the noodle leaving slighly more in the front and a bit less in the back. sit straight and pedal, like on a bike. use two straws if more than 75kg.
for easy swimming lessons in adults who may be scared of water: again, put the straws between legs and lie down supporting your arms on the straws. nice floating while legs and hands can be used to move about in the water.
lazy way: put the straw behind your back, bend and support your back and arms, like on an armchair.
there are many ways to use the noodles/straws. they are bendable and they offer good resistance. as i say, a heavier person, especially when they are learning how to swim and have little confidence, should use two of those. if you know how to swim and you are comfortable in the water one is more that enough to support your weight.