Yeah, like springfield said
you need to write specified bytes to a specified address, this will NOP the instruction that for example stands for updating your player data etc.
Size is 2 because you are writing 2 bytes to the address (C390, C3 (first byte) + 90 (second byte))
How do you need to know the size to NOP an instruction ?
Well, its easy.
Lets say you have found a instruction in CE that makes your player die if he blablablabla
The address is like 0x77B77 or w/e, in CE you will see that when its not NOPed it has a value like:
"68C17BC3"
So, we see that it has 4 bytes (1.68 2.C1 3.7B 4.C3)
To NOP it, we need to replace every byte with a NOP so the instruction will do nothing.
So we should write "90909090" to that address to NOP it (well in SA-MP patches there are sometimes other bytes than 90, i dont know why (not experienced enough xD) but for basic things like NOPing the instruction that changes your current hour (hehe) you just replace every byte with 90 and thats all.