Not every city has apps like One Bus Away or other similar apps, but most agencies have shared their GTFS data with Google to use with their transit function. I can personally attest to how well this feature works and how valuable it can be. I do consider myself an advanced transit user, I can figure out how to get somewhere with an address and route book, but that’s time consuming. Google transit allows me to simply plug in a destination and a beginning address and then spits out all of the possible combinations. I can even tell it; fewest transfers, least walking, or fastest route. One key thing to determine is if your arrival time is important. If it is then plug it in, if not put in the time you plan to start your trip.
If you are in a city you are not familiar with it will even give you walking directions. If you don’t own a smartphone with Google Maps you can still print directions out at home. Recently I was in Denver, and I’ve NEVER used transit there but I was able to navigate around. In fact as I’m typing this I’m riding the HART Route 36 and I got my routing information using Google Transit. Granted a bus tracking app would come in handy to use in conjunction with Google, but for now I’m happy to have at least one.