is either someone told you face to face or someone posted it online and you read about it, this was how Bitcoin became popular and I believe same thing will make it more popular and more valuable than it is now and is part of the factors that can make Bitcoin hit $500k and above.
Bitcoin has gained it popularity that right now you don't really need to tell people what bitcoin is all about. So far as one has access to the internet you will definitely know about Bitcoin, it is left for one to make a further step to doing more research to acquire understanding of what bitcoin is all about. Then when bitcoin haven't gotten popularity you have to preach bitcoin to people and trying to convince to just accept Bitcoin, but right now we have the internet that can give a better awareness of bitcoin and people can see for themselves how bitcoin have existed and got to the point where it is now.
Before now, there was no enough awareness on the internet which their was need people still need to bitcoin, but bitcoin is all over the internet and people just make their research to see what it is all about and make their decisions without anyone try to convince to accept Bitcoin.