Section is something that is written in the law and generally doesn't go under change usually. Rules are the thing in which the whole procedure or methodology of the implementation is written. It may underchange depending upon the condition.
In addition to above Rule is procedure how to do. means Section prescribes what to do & rule lays procedure how to do. Rule cannot be frame without Section & cannot override Section.
Sections are part of Act which is passed by the parliament (legislature). Rules are made within the framework of sections by the Government (executive). Sections are the basic legal framework while rules are instructions on how to implement and follow those framework.