Difference between act and rules

In Layman’s Term

Act says, “What to do” (i.e. provisions of the act)

Rules says, “How to do” (i.e. prescribed procedures)

In the constitutional law it is well explained about the the three division of ruling the Government.., Executive.., Legislature, & Judiciary. There should be laws to run the machinery of Government.

A law is an idea, placed in bill form, which passed in both the Houses of Parliament and / or State legislatures, and finally signed, by President or Governor. Parliament or state legislatures pass legislation or laws. Before it's passed, it's usually referred to as a "bill." Once it's passed and signed by the president or governor, it normally is called "This Act" or "That Act."
Act is the official name for a bill that has been enrolled for presentation to the President or Governor. Each act is assigned a chapter number and is published in the Gazette.

There are two definitions of a rule.
In the Legislature, rules refer to the regulating principles or methods of procedure. And second is procedural Rules.
In the executive branch of state government, rules are operating principles