Frostburg is roughly around the halfway point between Pittsburgh and Baltimore, a little more to the Pittsburgh side but not by a huge amount. From Pittsburgh you can take I-79 south (be careful where it joins up with I-70 east then splits off again), then take I-68 east straight to Frostburg. Getting out of Pittsburgh will be the only hard part.
From Baltimore, take I-70 west then I-68 west straight to Frostburg.
All interstates involved are at least 2 lanes and are decent roads. Try to avoid rush hour traffic in either Pittsburgh or Baltimore. Other than that there’s not much traffic to worry about. I-79 is a flat and easy drive, as is I-70 coming west from Baltimore. I-68 is a bit hilly but it’s a good road. Frostburg is right off of I-68 so either way is simple to get there with very few turns. Getting out of Baltimore is pretty easy. Just take the road away from the airport, get on 95 north to get to the Baltimore beltway, take the beltway west to I-70, then take I-70 all the way to I-68. Getting out of Pittsburg is a bit trickier, but it’s not horribly bad (IMHO). I haven’t driven near Pittsburgh lately though. Try to find out if there is construction or any weirdness going on around there that might make your life difficult.
You will need a car to get around Frostburg.
There’s no train service that will get you there that I am aware of. There is a train in Frostburg but it’s a scenic steam locomotive, not Amtrack or anything close to that. There used to be a good restaurant in the train station, but it’s been at least 10 years since I’ve been there. I don’t know if it is still there.
You can probably get there by Grayhound, but I wouldn’t recommend it. Grayhound stops in every little town along the way. It’s about a 2 1/2 hour drive from either Pittsburgh or Baltimore (maybe 15 minutes less from the Pittsburgh side). I’d expect it to take twice that by bus.