Back in the days when there was Bitcoin and just Satoshi testing it, how did other early adopters of bitcoins came to know about it? Did he advertise about btc somewhere to attract people's attention to this new technology? How did bitcoin users initially rose from zero to millions ?
He didn't - no ICO or anything like that and imo thats what makes bitcoin special. The founder didn't create it for money, but rather he legitimately created it because he had a purpose in life. Sure he mined a lot of coins afterwards but there is nothing like a premine/ico that goes on.
Later though there were a few people that started spreading the bitcoin "gospel". Like Roger Ver.
These days alts are too saturated, everyone is in it for the money.