SAP APO Deployment

Hi Experts,

I am new to SAP APO and I am not clear about deployment heuristic as it is confusing me.

I've already gone through some of the below threads regarding distribution rules

deployment fair share rules

Heuristics and Deployment

Deployment Heuristic - Deployment - SAP Library

Can anyone please shed some light on deployment, Rules,Horizons.(Also plz suggest any books where i can understand easily)

It would be really helpful to me .

Thanks in advance.