Someone can specify about this better than I can... You've got ignition timing right. Advanced timing=higher cylinder pressure + more power
Retarded timing=lower cylinder pressure + more after-burn.

^This is all related to ignition timing.^

As far as valve timing is concerned, you can index your cams to open or close the valves earlier or later. Where this happens and how it benefits you is really dependant on the hardware you're working with. Varying valve timing affects when the gasses enter and leave the combustion chamber. Opening exhaust valves too late will roast exhaust valves. Closing intake valves too early will lower your compression. Closing them too late can cause back fires (God forbid you have a sheetmetal intake manifold). The objective is to keep the overlap of the valves in a respectable limit so that you can flow as much air as possible without detonation, and achieve the best possible compression ratio. On a SOHC engine, it's not all that complicated... and IMO, not really beneficial.

For the most part, you want a machine shop to index your cams unless you have some means of data logging and have done it before. You should also dyno tune the car to make sure you got it right. Changing the valve timing affects the ignition timing. They work hand-in-hand.

But like I said. Someone else can explain it better. My ignition timing is electronically controlled, and the only cam gear that benefits my 4g63 is the exhaust cam. Usually less than a 3 degree adjustment. So I don't have to be as careful as someone with a pointed distributor system would have to be with this.