So, like, where is Serbia, like, exactly?

If you never heard of Serbia, don't despair.

You're not stupid or ignorant, just a little uniformed about southeast Europe. Because, yes, that is where Serbia is roughly located. More precisely, it lies on the Balkan Peninsula, alongside Greece, Bulgaria and Albania to name a few. I won't bore you with the geographic info (find everything relevant in this wikipedia article), and instead, give you some traveling references.

The flight from London to Belgrade (Serbia capital) should last around 2 to 3 hour; Frankfurt-Belgrade should be a little shorter. You will have to travel at least 24 hours by bus from any northern European capital (Paris, Brussels, Berlin) to get to Serbia; train should get you here a little faster. Car is by far the best ground-based option, but journey time depends on your driving skill and the traffic. Let's just say that it's possible to get from Belgrade to Vienna in 7 hours, but you have to be rally driving material.