'die Flagge' vs. 'die Fahne'
What is the difference between die Flagge and die Fahne?
The verb erfahren can also mean 'to hear'. But what is the difference between erfahren(to listen), hören and lauschen?
To your first question: In everyday language both "Flagge" and "Fahne" are equivalent. Technically speaking, "eine Flagge" is used for signals (e.g. stopping traffic at roadworks or a level crossing with a red flag; semaphore flags...) while "eine Fahne" is used for identification (e.g. the flag of a nation or an army). Furthermore, "Fahne" is used in slang if someone smells of alcohol: "Der hat eine Fahne."
I am not sure wether I understood your second question in the right way, but I'll try... "Hören" is used, when you hear something wether you want it or not - music, talk, any noise. "Lauschen" is used, if you hear/listen actively and in secret. So if you put your ear at a door to get to know what is said inside or use a hidden microphone, it is "lauschen". "Hören" kann also mean, as you said right, "to get to know something": "ich habe gehört, dass er krank sei." = "I heard he was ill". Here you can also say "Ich habe erfahren, dass er krank sei."
Hope I was able to help. Some things in German language are complicated, even for a native speaker...
Forgive my use of English. I believe „hören“ and „erfahren“ are only synonyms in the same way that "to hear" and "to find out" are synonyms like the brilliant example Steffen185372 gave: „Ich habe gehört/erfahren, dass er krank sei.“ and that in those examples, the difference is the same as the difference in English between "I heard that he's sick" and "I found out that he's sick".