Basically anyone who ever set foot in the U.S. is 99.9% guaranteed to be found electronically now. That will take you to where they came from and in most cases that original generation will be known. Since people did not travel much (as we know it today), chances are they are mostly from that place , wherever it is, for some time back. Thanks to Napoleon (you don't thank him much, do you?), standard records have been kept across at least Europe back to their inception in ~1810. Prior to that, records devolve into individual church parishes and are mostly in Latin. It is super easy to pick up the Napoleonic civil record format in any language. I never could quite grasp the hand-written ink-well pen Latin records of the late 1700s so I don't know how much further back I will be able to go.

I do have to give a special shout-out to the Polish national archives as well as the U.S. National Archives people in Maryland. I was able to deal with the Poles entirely online and request hundreds of records which they reproduced for a reasonable fee in a short time. The U.S. archives also went out of their way to help me. Hell, even the FBI FOIA process worked well and gave me a valuable dossier. The one awesome lead that let me down was the NYPD FOIL request I made. A relative many generations back ran with Al Capone when he was in Brooklyn and was gunned down. The NYPD never caught the killer and supposedly had a hat left at the scene and other evidence. Murder investigations are kept indefinitely so they should still have it in some warehouse somewhere, but they couldn't find it after searching for it manually. (Digitize all the things, people!)

(Not the person you were asking)

It depends on your heritage (I am of northwestern European and American descent, so my records are very good) but Ancestry makes it very easy, to their credit. A few minutes after you've added a new family member, Ancestry begins suggesting historical records and public trees (I try to avoid relying on the latter) that may reveal additional information about them, including who their family members are. You then mark which information to import.

So essentially you would start by inputting the family history you know, and then let Ancestry start making suggestions. It still takes plenty of manual intervention but I've taken their suggestions back to the 1500s in some cases.