To clarify:

Field x is the field number to use to retrieve a value, starting at 0.
Line y is the row number to use to retrieve a value, starting at 0.

So in the case of:
1 Test1 123 887
2 test2 456 998

To get 998, x = 1 and y = 1. Test1 is row 0 and test2 is row 1. The numbers 123 and 456 are in field 0, which makes x equal 0. The numbers 887 and 998 are in field 1, which makes x equal 1. The numbers 123 and 887 are in row 0, which makes y equal 0. The numbers 456 and 998 are in row 1, which makes x equal 1. Hope this helps.