See the link that Jessica shared for information regarding confirming relationships with DNA here at WikiTree. That page describes the DNA confirmation process for matches that are 3rd cousin or closer, and provides a link to the Triangulation Help Page which describes the process for matches for which relationships are more distant than 3rd cousins.
DNA matching at Ancestry can't currently be used for confirming relationships here for which DNA matches are more distant than 3C, since segment triangulation is required, and Ancestry doesn't currently provide the necessary tools to view the matching segments that you have with DNA matches there.
If you've tested at another DNA testing site that provides segment matching tools and/or if you've uploaded your AncestryDNA results to one of those sites or to the 3rd-party GEDmatch site, you can use the segment matching tools at those sites to evaluate segment matches with your DNA matches at those sites. See the triangulation help page for more details.