I’ve been working on my family tree for decades. When I took the AncestryDNA autosomal test, the ethnic results matched my expectations, with mild variations. I knew my mother was of completely Irish heritage, but I came up 58% Irish, so apparently some of Dad’s British ancestors were Irish, not English, for instance. The section that matched me to other DNA test-takers was also accurate. I recognized a couple of my second cousins listed there. Other people had taken the test but hadn’t created a family tree, so there was no point in contacting them to figure out which ancestors we had in common. Be sure you’ve done some research on your own family–these kits do NOT tell you where you grandparents came from, or their occupations, or their names. They tell you how much of your DNA is common with certain nations or areas. I know I have some Germanic ancestors, so when my kit said “14% West Europe” and that turned out to include Germany, France, Netherlands, Belgium, Luxemburg, and Lichtenstein, it made sense.
Specific tests for your father’s family include ‘Y-DNA’ tests which focus on the ‘Y chromosomes’ in your cells’ nuclei, passed down from father to son. Specific tests for your mother’s family include ‘mtDNA’ tests which report on a subset of DNA found in the ‘mitochondria’ (your cells’ energy factories), passed down from mother to son or to daughter.