In most Indo-European languages, verb tenses indicate not only the time at which an event happened but also whether the quality of the action was continuous, frequentative, or punctilinear. Proto-Indo-European distinguished six basic verb tenses, a present, imperfect, aorist, perfect, pluperfect, and future. As languages of this family evolved, they tended to have increasingly less complex verb structures. Homeric Greek, for example, distinguishes four different past tenses, a pluperfect (completed action in the past, often occurring before another action in the near past), perfect (completed action), imperfect (continuous action in the past, perhaps continuing to present), and frequentative (e.g. the "sigma-kappa" frequentative of Homeric Greek, indicating an action repeated multiple times), whereas in classical Greek and Latin the imperfect is used both for continuous and iterative actions. In Classical Greek, the aorist indicates a punctilinear action as opposed to the perfect (a completed action) or an imperfect (continuous action) or pluperfect (earlier completed action)
In English, verb tenses are more limited, and often use auxiliaries to indicate aspect. A simple past "I walked" indicates that the action occurred in the past, but it could be continuous or punctilinear. A verb in the perfect tense indicates an action occurring at an unspecified time in the past
"I have walked to the store, but I usually drive." Note that the time at which I walked is not specified, nor whether it occured before or after the driving.
Pluperfect is a specific time in the past earlier than another past event. "I had walked to the store and back before my friend showed up to give me a ride."