As represent negatives hexadecimals numbers

[h8er]

The x86 architecture uses the two's complement for negative numbers, to calculate the two's complement of a number you calculate the one's complement and then you add 1.
So for a signed 32 bit dword value you calculate the bitwise NOT of it and then you add 1.

For example the number 34d is 0x00000022h so

-34d = (NOT 0x00000022h) + 0x00000001h = 0xFFFFFFDDh + 0x00000001h = 0xFFFFFFDEh

I advise you to read The Art of Assembly Language, it's a good start for learning assembly