Auslan signs can blend with other signs or modify their movement to create a new meaning. The root sign, or in some cases location or hand shape in a location can thus be likened to kanji in Japanese (base level written word) that can be blended or added to, too change the meaning.
A "radical" (coming from "radix" meaning root in Latin) in linguistics is a root word, suffix or prefix that hold meaning and can be added to a word, or forms the root of a word that allows us to interpret meaning. For example unicorn, unicycle, an unique all have a meaning associated with one (uni meaning one or single)
By understanding the most popular radicals in Auslan you will start to be able to guess meanings of unfamiliar signs.