Things happen. We appraise them, assessing them against various criteria. We then feel emotions based on those appraisals.
We do this in real-time, appraising and feeling as we go. We also do in reflectively, thinking further about what has happened and what may happen. When we think of the past or future we hence may feel good or bad about it.
Primary appraisal is an assessment of how significant an event is for a person, including whether it is a threat or opportunity. Secondary appraisal then considers one's ability to cope or take advantage of the situation.
A structural model of appraisal describes the relationships between:
Perception: The environment and the person's perception of this
Appraisal: The person's appraisal processes that evaluate the perceived environment in terms of values on a set of measures called appraisal dimensions.
Mediation: The processes that relate appraisal values to the person's emotions.
A process model of appraisal describes the detail of cognitive operations, mechanisms and dynamics by which the appraisal happens. In other words, the structural model is the static map and the process model is the dynamic operation.
This is a cognitive approach to understanding emotions. Other theories view emotion as more reactive, without the opportunity to think. Indeed, we sometimes do not get the chance to think, for example when a fierce creature leaps out at us and we react with animal instinct that short-circuits the slower cortical appraisal. However, such reactive emotion is not necessarily how we feel in all situations.