How do witches/wizards from Muggle Families RSVP to acceptance announcement?

[mspond1 at aol.com]

No: HPFGUIDX 23147

My daughter came up with an excellent question yesterday.  If someone 
(like Hermoine) gets a letter inviting him/her to attend Hogwarts, 
but he/she is from a Muggle family, how does he/she know how to 
communicate with Hogwarts?  

How did Hermoine know how to get to Diagonalley to purchase her 
supplies?

Does anyone else see a little romance shaping up for Hermoine and Ron 
at year 7?  The Weasleys are fond of muggles, so they wouldn't have 
the in-law problems at least!

Marilyn