How are homologous structures such as forelimbs evidence for common ancestry and change over time?

They represent similar patterns through ancient fossils and living animals today, such as the relevance of the one bone, 2 bone, many bones pattern found on the human arm bearing minor resemblance to tiktaalik's structure, and major resemblance to lizard, cat, bat, and frog structures. -- this may not be 100% however expand on that and maybe do additional research to develop a more percise response to the question.