Doctor Who 50th Anniversary

That awkward moment when it seems like everyone in the Tumblr-sphere is excited about Doctor Who, and you want to be excited with them, and you've wanted to watch and get into the series for a long time now, but no one you know watches it because you live in America, and it's not as popular over here, so you have to live vicariously through the people on Tumblr and....

Hasn't this show been on for 50 years?

And there's been 11 Doctors?

Where the heck do I start?

What is the blue police box TARDIS? Why does he carry around a "screwdriver"? How can they just keep changing actors like they do? And what does the Doctor actually do? Is he human? Is he some sort of superhero who saves the world? What time period is he from? Why is there only one Doctor guy? Is it just this world, Earth, or does help dozens of planets and species? Can he travel across space and time, or just time?

This is all very confusing to a noobie like myself who sees bits and pieces on BBCAmerica and Tumblr...