There are many sites online providing links to census records, marriage, death, and birth records, wills, land records, and many other documents one needs to properly build out a family tree. Many of the larger sites cost quite a bit of money for monthly or yearly subscriptions, but several sites are totally free to use. I personally use FamilySearch as my first go-to resource, but there are many other webpages, as listed in this article "50 Free Genealogy Sites to Search Today".