Deuterostomes represent a major branch of Animalia as do protostomes. Most of the animals with exoskeletons would be protostomes while those with endoskeletons are deuterostomes.
In early embryonic development, which is believed to parallel evolutionary development, the single cell splits several times until eventually, the clump resembles a hollow sphere. Then this sphere caves in on one side, making two layers of cells and becoming bowl-shaped. And then, the bottom of the bowl opens up to resemble a short tube.
NOW, the difference between us and bugs is the first (cup) hole becomes the anus in deuterostomes (us) and the second hole the mouth, while in protostomes (bugs, lobsters, etc.) the first hole is the mouth and the second hole the anus. So the difference is very basic, going back a half billion years or more in evolutionary history. And yes, we are basically donut-shaped with the alimentary canal forming the hole in the donut.