I'm honestly quite surprised that you've never even heard of the likes of Senna or Schumacher Until now I was under impression that even those who had absolutely no interest in racing and motorsports still knew those household names!
Anyway, the answer to your question depends on whom you ask. One thing you have to realise is that the sport has changed so much over the years that there's no way to rate drivers over different eras objectively and so comparisons across generations are pretty much useless. Different cars, different attitudes and mentality, different technology, different standards; just a different racing culture altogether. As an example, it's one thing to drive a heavy death trap of the 60s and 70s with no power steering and help from the team garage on unforgiving tracks with poor safety standards, a completely different one to drive a modern heavily aerodynamics-reliant F1 car with all its subtleties, the electronics and driver aids and constant team feedback over the radio where the driver has to do a lot of information management in the cockpit.
Rating the drivers based on the era they raced makes more sense I think. I'm only following F1 properly since late 80s/early 90s so can only judge the previous generations based on some archive footage, stories I've heard and books I've read, but that's how I'd do that:
50s - Fangio
60s - Clark
70s - Lauda
80s - Prost
90s - Senna
00s - Schumacher
10s - Hamilton
The list still misses a lot of extremely gifted drivers; Mansell, Piquet, Häkkinen, Alonso, Stewart, Moss, Patrese, Hill to name a few big ones.
My personal list from the ones I followed closely would be Schumacher - Senna - Prost - Hamilton. Michael will always be #1 for me (for numerous reasons; some of them being objective, some very subjective) but I'm putting that list in no order otherwise. Hamilton is definitely the best driver of his generation, only Alonso comes close to him in my opinion.