Platform 9 and three quarters and other muggle born wizarding questions

[Tamara]

No: HPFGUIDX 45973

Okay, when Harry went to get on Hogwarts Express for the first time, 
he would have never made it if it hadn't had been for Mrs. Weasley.  
So my question is, what about other muggle born Hogwart students?  It 
seems the info about the platform wasn't included in the welcome 
letter, neither was the info on Diagon Alley and wizarding money 
etc.  How do they find this stuff out?!