There are different types of DNA tests available. With law enforcement, they tend to use STR markers, used to be 13 to a couple of hundred markers. Same for parent/sibling tests. For genealogical DNA testing, there are several options – autosomal done by the major DNA companies like AncestryDNA. These tend to be SNP tests, ranging from a bit under 100K SNPs to as high as over 930K SNPs if you tested with the old v3 chip from 23andMe. Other options are Y-DNA (males only), mtDNA (males and females, but the males don’t pass it onto their children. Only a few companies do Y-DNA tests and fewer do mtDNA tests. Specific DNA markers that vary by DNA company. Some companies do health and other types of trait or medical testing.
The major DNA companies show ethnicity results, but below the continental level, it becomes iffy at best. Some companies compare your DNA to famous people. In some states and countries, there are restrictions on some types of DNA tests. Determining gender of an unborn child is not allowed in a few countries. Determining paternity is not allowed in several countries. For parent tests, you may need to use an in-person local lab as courts want to make sure the people testing are really who they are supposed to be. For informal results, it’s cheaper to do a $79 – $99 test to determine if a child is yours. It’s not admissible in a court of law, but it would be a lot less expensive than paying for a court ordered test. If the child turns out not to be your children, then you may be able to petition the court to order a DNA test.
If you have a fair amount of money you aren’t using for other things, you can test pet DNA. Cat, dog, snake, bird, horse, etc. Prices can vary a lot between different companies.