A set of ordered pairs form a function if all the
x-coordinates (first coordinates) are different,
and no two are the same.  It doesn't matter if some
or all of the y-coordinates or second coordinates are
the same.

1. (4,1)(3,2)(2,3)(1,8)

That is a function because all four x-values, that is,
x-coordinates, or first coordinates, 4,3,2,1 are all 
different.

2. (1,3)(2,3)(3,3)(4,3)

That is a function because all four x-values, that is,
first coordinates, 1,2,3,4 are all different. 

[Notice there that it doesn't matter that the y-values, 
that is, second coordinates, 3,3,3,3 are the same.  Only 
the x-values, or first coordinates must be different in 
order to have a function.

3. (1,1)(2,2)(3,3)(4,4)

That is a function because all four x-values, that is,
first coordinates, 1,2,3,4 are all different. 

4. (2,1)(4,2)(5,3)(-2,4)

That is a function because all four x-values, that is,
first coordinates, 2,4,5,-2 are all different.

5. (8,1)(8,2)(8,3)(8,4)

That is NOT a function because all four x-values, that is,
first coordinates, 8,8,8,8 are NOT all different.

6. (-2,-2)(0,0)(6,6)(-8,-8) 

That is a function because all four x-values, that is,
first coordinates, -2,0,6,-8 are all different

Edwin