I found this on their github site:
Updating records
To update the database, change one or more of the properties of the object, then call the save method to commit the changes to the database. Again, you can change the values of the object's properties either by using the set method or by setting the value of the property directly:
$person = ORM::for_table('person')->find_one(5);
// The following two forms are equivalent
$person->set('name', 'Bob Smith');
$person->age = 20;
// Syncronise the object with the database
$person->save();
Creating new records
To add a new record, you need to first create an "empty" object instance. You then set values on the object as normal, and save it.
$person = ORM::for_table('person')->create();
$person->name = 'Joe Bloggs';
$person->age = 40;
$person->save();
After the object has been saved, you can call its id() method to find the autogenerated primary key value that the database assigned to it.
Checking whether a property has been modified
To check whether a property has been changed since the object was created (or last saved), call the is_dirty method:
$name_has_changed = $person->is_dirty('name'); // Returns true or false