Syntax for use of point

I have made the table shown below and inserted two points,
but I can't find the proper syntax for finding the nearest point

create table store_point(position point);
insert into store_point values ('55.512345, -6.55555');
insert into store_point values ('55.123456, -6.11111');
select * from store_point;
        position
----------------------
  (55.512345,-6.55555)
  (55.123456,-6.11111)

I suppose that I should use the ## operator,
but how does it work when I want to find the nearest
row for the points (55.4,-6.4) ?


Thanks,
  Poul