Something that's associative involves connections between things, especially ideas or processes. An associative memory, for example, might come from a scent that your mind connects with a specific place you visited as a child.
Although you can use the adjective to describe all kinds of things that are characterized by the idea of connection or association, you're most likely to find it in scholarly writing. In psychology or neuroscience you might read about "associative learning," in which a certain behavior results in a stimulus — a reward or punishment. The association between the action and the result makes this kind of learning associative. The Latin root is associare, "join with."