The habitable zone is the zone where liquid water may exist on the world. Earth, for example, is in the HZ. For a world to meet the prison code criteria, atmosphere needs to be 2,3,A, or B. Hydrosphere needs to be 10 to 50% (1-5). Population level should be 3-6, and the government types 6-9. For the original Big Black Book (T5 BBB) it does NOT need to be in the habitable zone.
First, use page 432, table 2, and make a flux roll. Look at the habitable zone (HZ) variance column to learn the HZ, and see the definition in table 3 to see what they mean. HZ-1 is closer to the sun, HZ is in the "perfect" spot, and HZ+1 is father away from the sun.
Proceed to page 434, for the remarks. Secondary remarks DO NOT apply to the mainworld (MW), except for the prison world designator. Habitable zone does not affect anything except a farming world. under those secondary codes, and again those do not apply to the MW.
HZ comes into play on the CLIMATE portion of the table. If a MW falls into the HZ-1 category, it is HOT. If HZ + 1 then the planet is further out, and therefore colder.
For what it is worth, I feel the Garden World designator under the Planetary section should specify HZ only; I could possible see in for HZ-1 for a tropical world.
Hope this helps.