Read this summary of using DNA to find biological family at ISOGG – https://isogg.org/wiki/Utilizing_DNA_testing_to_break_through_adoption_roadblocks written by the DNA adoption people.
There is a wealth of material at DNAadoption.com and they also have online classes on how to use DNA in your search. In addition, there are yahoo mailing lists just for adoptees at http://groups.yahoo.com/neo/groups/dnaadoption/info . Plus there is a group of Search Angels willing to help you out with your basic Adoption search. Find out more at http://groups.yahoo.com/neo/groups/SoaringAngels/info
Also the DNA Detectives Facebook page is a great resource for those with unknown parentage. They have over 50k members helping each other – https://www.facebook.com/groups/DNADetectives/
Anyone with 2nd cousin matches at Ancestry.com can try the mirror tree technique to figure out which line they are related on – see how here http://www.borninneworleans.com/how-to/what-is-a-mirror-tree/ although using GWorks (see below) might be easier.
This article from Leah Larkin, the DNA geek is a terrific summery of the testing process:
Finally I have a number of posts here. Click here for my post which outlines the steps to use the DNAgedcom tools set called GWorks – http://blog.kittycooper.com/2017/09/solving-unknown-parentage-cases-with-dna/ which uses automation to compare the trees of your matches.