okay, may I go for something not as funny for the people around?

Speak English and alook out for "Bus to Bonn main station" or take a printout with you with checkmarks where you can point at:

"Suche den Bus nach Bonn Hauptbahnhof."

[to confuse you about zu / nach - to the bonn main station would be zum as main station is the thing, "nach Bonn Hauptbahnhof" is in fact the short not very correct version of "nach Bonn zum Hauptbahnhof".

I would assume you see signs there guiding you to it.
Try to have little change with you like a 10 Euro bill max for buying a bus ticket. Check out the web sites of Bonn, you can expect this to have english translations due to the time of being capital.

You will find Bonn to be a funny mix of international flair and small city due to that as well.

Bonn itself is very nice and easy to get around, if you visit there do not forget a short trip to cologne for the Dom and some more - you can actually enter the bus anywhere in Bonn and buy a ticket to cologne right away.

You do have a mixed system of bus / train etc which is all linked together in a so called "verkehrsbund" aka system of transportation is locally linked.

the websites should explain that much better.