What are fossils? What are the advantages of studying fossils?

Read the below paragraph and answer the given question.

Speciation refers to the origin of new species from pre-existing species due to the accumulation of large inheritable genetic changes called mutations. Speciation occurs when the gene pool (sum of all the genes of all the members of a species) of a population is somehow reproductively isolated from other sister-populations of the parent species and gene flow no longer occurs between them. Then a population splits into two independent species which become reproductively isolated from each other.

What is meant by speciation? How does it differ from microevolution? Briefly explain the steps of speciation.