SoulSurfer

Ok I hear a lot of people talking about tuning their engine when they do upgrades like a JG Edelbrock intake manifold. Being a newbie with little mechanical background Im just curious what "Tuning" entails. Anyone know where I can find some good info on what might need to be tuned on a B18B with DC header, intake, cat back, and intake manifold (soon to come)?
I did a search and didn't really find the answer I was looking for.