How exactly did organisms evolve through evolution?

I have been always wondering about how evolution is explained? How did certain organisms evolve into different types of species? It's weird, but certain animals have similar appearances with other animals. I noticed the crab has eight legs, claws, and moves in very fast paces in diagonal directions that lives in the sea and the shore. There are other animals that have a very similar appearance to these creatures, spiders, but to be more specific, tarantulas. They have similar appearances, and they walk in the same pace and direction. Did the spiders evolve from . What about lobsters? They have several legs, long and narrow bodies, claws, and stings. The other animal which appears similar are scorpions. They have similar appearances and walk in same paces and directions. These shellfish and insects also seem to have this unusual skin texture, skeletons on the outside, hair. Isn't this the similar theory as human beings relating to apes? What about the cats relating to tigers, lions, in the feline family, or the dogs relating to the coyotes and wolves, in the canine family? It's weird, but human beings don't really look like they've evolved from apes. This is just my opinion. The apes don't seem to have noses like human beings, but this is just my opinion. There are so many organisms which share very similar traits to each other. Lastly, it is haunting, but I always thought that aliens are related to certain organisms, most likely to the octopuses. They have the same round, large, long heads, tentacles, slimy skin texture, similar shaped eyes, and they both move in a very unique style. Anyways, this has always interested me. Please let me know about your opinions. Thanks.