Takes an existing object it populates it with information from the database. Does not populate any children. For that, use LoadWithChildren.
This will overwrite any properties that are already populated in the existing object. For example, if you've set customer.FirstName = "John", it will be changed to "Bill" once you load the object with record #1.
Example:
Customer customer = new Customer();
IObjectMapper<Customer> mapper = Elementary.GetIObjectMapper<Customer>();
mapper.Load(customer, 1); // all properties are now populated except for child objects