I need to query a record from account with below filter criteria:

Select Id, name, billingpostalcode from account where name = 'xyz account'



 

I have data in the External Database and with the help of Salesforce connect I am able to connect with this External DataBase and I am able to see the data.
 
Before Making Connection I have some question 
 
Question 1)Once  Salesforce Org  connect with external system, are we duplicating the same data that exists in External Database and storing the salesforce Or just we are getting the  copy of the External data into the salesforce ?
 
Question 2)Suppose if any data/record updates in External Database(from there end)
 Will the new data replicate in salesforce or It will show  the Old data?
 
Similarly In salesforce org if I update any data that belong to external database, Will that new data replicate in External Database immediately.
 
Can anyone please clarify these questions...