There are many reasons as to why a person should look for a DNA test for adoptees but some of the basic reason for getting a DNA test falls under three categories:
Since DNA segments that are close to each other on a chromosomal arm and more likely to get inherited together, the genetic markers (chromosomal markers) that are present on it also get inherited. These genetic markers are then used to identify the closest possible link between the DNA samples and determine the genetic link between individuals.
The results are also good at telling how close you are related to a person genetically that is the percentage of DNA you have in common with the other. Which can ultimately tell how close you are related to someone. They can also determine whether you are a close relative like a sibling, Parent Grandparent, or distant relative like Aunt, cousin, etc., by comparing your DNA.