Well the last few posts are right, but I'll just post this again, originally from Post #20...
The idea of the game is to think of a word that 'contains' those 2 letters.
They can be spread apart or be next to each other and be in any order, but not be exclusively used as just the first or last letter of your new word.
If you look at 3 of the previous posts above: #13 #14 #15. The letter Y is used for the end of the word rather than inside the word.
For example, the 2 letters from post #14: P Y, could be used in the word 'Gypsum' or perhaps 'Papyrus'.
In the case of 'Papyrus', although it starts with the P, that letter is also inside the word.
(I hope I've not made it seem more complicated than it really is)...