if say a relation has a value pairs of say
(a,b),(c,d),(e,f),(g,h),(i,j)
the the value pairs for its inverse will be
(b,a),(d,c),(f,e),(h,g),(j,i)
notice, is the same pair, but flipped sideways.
and of course, the domain is the set of the x-values or the x-coordinate or the first value of each pair, as you already should know.