Inside a function or any where add below code :

add_user_meta(‘userid ”new_field_name’,’value’);

eg:
add_user_meta(‘1’, ‘bonus_points’,’1′);

Getting value from this field:

$user_current_points = get_user_meta(‘1’, ‘bonus_points’,’true’);

updating field:
update_user_meta(‘1’, ‘bonus_points’,’20’);