ancestry.com & familysearch.org are repositories of genealogical data. They are not standalone genealogy software.
PAF, RootsMagic, Family Tree Maker and 100's of other programs are software that will sort your family information into recognizable chunks. You can import or download information from Ancestry or FamilySearch, but beware, just because it's linked, doesn't mean it's accurate.
Do your research. Document your sources. It's much easier to do today than it was 10,50,150 years ago, but mistakes (and lies) still happen.
GEDCOM, btw, is a format for universally exchanging genealogical data between programs. Makes it much simpler to "get a copy" of Uncle Fred's data, when he can burn a disk or flash drive. (Get copies of his sources, too. He's not going to be around forever!)
YMMV