In English we have two ways of forming the past tense.
1. Add the “-ed” suffix to the word:
I laugh at Elliott’s jokes (present).
I laughed at Elliott’s jokes (past).
2. Change the form of the verb:
Zach runs down the court (present).
Zach ran down the court (past).
Comparison with Greek
Like English, Greek forms the aorist in two ways.
The first aorist is formed from the present stem with an augment and suffixed sa. The second aorist is built from a different aorist stem but both aorists take an augment and add second active personal endings that are identical to the imperfect forms.
The aorist is the most frequently used tense in the New Testament. Both the first and second aorists are usually translated as a simple past (e.g., he came, or he comes). The two types of aorists function in exactly the same way in sentences. The second aorist is presented first because of its similarity to the imperfect.
The aorist is used when the action is viewed as a whole and complete (e.g., he loosed). The aorist is the most frequent tense form and is used as a background tense by writers as opposed to the present tense form which is used to foreground material. The imperfect is used for continuous/durative/iterative (aktionsart) or “dwelled upon” (aspect) action (e.g., he was loosing). The actual time or tense of the action is triggered more by temporal pointers like adverbs, prepositional phrases and conjunctions than the aorist tense form itself. The aorist can be used for actions which are past, present, omnitemporal or timeless. Thus, the aorist is extremely flexible. For our purposes we will initially just translate it as a simple past (e.g. he loosed). While the endings parallel those of the imperfect, note carefully that the second aorist stem is different. There is no way to predict how the second aorist stem is formed; thus, it must be learned by memory. First aorists use the present stem.