Need quick explanation about FETCHING

Need quick explanation about FETCHING

Hello,

When I fetch records, for example :

Variable = CustomerForm[ID != null]

Are all the fields of the CustomerForm included in the variable or only the ID ?

Another example:

Variable_2 = CustomerForm[City = Chicago]

Will I access to the full adress of my customers in Chigago using Variable_2 ?

What exacly is stored in those variables ?

Sylvain