SOLDIERX.COM Nobody Can Stop Information Insemination

Currently enrolled in PWK for obtaining OSCP cert from offensive security. Would like some people I can hit up via email (preferred) or IRC for pointers while trying to figure out this grueling course. Have decent level of C and Python knowledge, but buffer overflow understanding is kicking my ass.

First question would be: Any good resources for understanding why a NOP sled is necessary when sending a payload (like slmail exploit or crossfire on linux side) went through tut a few times still not understanding why the NOP sled varies "\x90"*8 or "\x90"*16 both work????