What is difference between ToList() & AsQueryable()

Question

please tell me What is difference between ToList() & AsQueryable() ?

 

see the code with AsQueryable()

var source = (from customer in _context.CustomerTBs.
                OrderBy(a => a.Country)
              select customer).AsQueryable();

 tell me when above code will execute then records will be fetch from db or not ?

 

var source = (from customer in _context.CustomerTBs.
                OrderBy(a => a.Country)
              select customer).ToList();

 when to use AsQueryable() and when to use ToList() ?

 

looking for  answer in details. thanks