How is a schema related to constructive processing?
A schema (plural schemata) is any pattern of thought, idea, or habit that exists in a structured form (Wikipedia). Constructive processing is the conscious examination and absorption of outside stimuli that results in either knowledge gained or action taken. To associate the two, it must be understood that schemata rely on both preconceived knowledge and the addition of new information to existing structured patterns.
Basically, when a person encounters an idea or situation, the new information is automatically compared to and filtered through existing schemata; a fire is considered hot and dangerous because past experience of fires is located in the "Dangerous, Hot" schema. The conscious decision to stay back from the fire comes from the constructive processing of the external stimuli: it looks hot, and feels hot, so it is dangerous. The schema also allows new action based on the new information: while it looks dangerous, it is also confined to a small area, and so it is safe to remain nearby for now. Many, if not most, of these decisions are made unconsciously, since the schema structure works too quickly to assess based on the existing knowledge.
Schemata can also work to alter memory or perception of situations; if there is an existing schema that associates clowns with bad memories, a phobia of clowns based entirely on the schema can result. This is an example of confirmation bias; the negative feelings exist because of the associations, and are reinforced by the unconscious memories or feelings as filtered through the schema.