Find an available Seats which are adjacent to each other?

I found the following question in one blog. i am unable to find the logic. Please help me here.

The question is: Find an available Seats(Status – ‘y’) which are adjacent to each other.

CREATE TABLE tbl_MoviePlex (Seatid INT, Status CHAR(1))

INSERT INTO tbl_MoviePlex VALUES

(1,'y')

,(2,'n')

,(3,'y')

,(4,'y')

,(5,'n')

,(6,'y')

SELECT

a.Seatid

,b.Seatid

FROM tbl_MoviePlex a

INNER JOIN tbl_MoviePlex b

on a.Seatid = b.Seatid + 1

and a.Status = b.Status

What is happenning at on a.Seatid = b.Seatid + 1 ?