Imperfect in German is not used as often as perfect (past perfect tense), but literary works cannot be read without it. Indeed, in the book language the form Praeteritum is most often used.
What is the past tense form?
In German, Praeteritum (“preteritum”, also “preterite”) is used to denote past events. From the Latin language, the indicated word is translated as "passed by." Also, this form can be called narrative time. If the Perfect is used primarily in colloquial speech, then the preteritum in German is characteristic of book speech. When an extensive coherent narrative (book, novel, story) is conducted, Praeteritum is also used.
When Preteritum is Used in German
It is believed that the difference between the elapsed time and the perfect is that the Perfect is somehow related to an event in the present tense. Since in colloquial speech almost all events are connected with the present (there is no sense in saying that it doesn’t matter), in everyday life the past perfect tense is mainly used. The role of book time, the language of the media, remains the preteritum. It is also used in stories of past events. For example, a person talks about what he did in the summer, last year / decade, etc. And then, since this form is rarely used, it already sounds too literary. Therefore, even in first-person stories about past events, the past perfect tense is often used - Perfect.
Imperfect in the German language is also used today along with perfection if the verbs haben, sein, as well as modal are used. For example, the phrase “I was at the institute yesterday” will be translated as Ich war gestern im Institut rather than Ich bin gestern im Institut gewesen. And in the sentence “The child wanted a present for Christmas”, the verb in the simple past tense will be used more likely. Das Kind wollte ein Geschenk zu Weihnachten (not Das Kind hat ein Geschenk ... gewollt).
Let's say a few words about how modal verbs change in the past tense. The umlaut in this case leaves, the suffix t is added. For example, the stem from the verb müssen (should) in the preteritum will sound like muss + t + personal ending. If there is no umlaut, then he, accordingly, is not added. Ich soll - Ich sollte, Wir wollen - Wir wollten.
How to form the past tense
Verbs in preteritum in the German language can be formed according to two different formulas. A simple past tense is formed using the suffix t, which is added to the base of the verb. We have the following formula:
Imperfect = verb stem + t + personal ending. This formula applies only to weak verbs.
An example is as follows: Ich studiere means "I study, study at a university or institute." But Ich studierte means "I studied."
If the stem of the verb ends in the consonants "d", "t", then between the main and the suffix of the past tense the vowel e is also placed - to facilitate pronunciation. So, Ich arbeite means "I work (now or generally)", but Ich arbeitete means "I worked."
It’s like Past in English, even the past suffix is similar - (e) d. And equally, as in the language of Shakespeare, in German there are irregular verbs. For irregular (strong) verbs, the formula will be different:
Base + changed base (for each different, you need to memorize it) + personal endings.
Preterite Features
It should be remembered that in the singular in the first and third persons the verbs coincide. This must always be kept in mind when using the preteritum in German. Suggestions for example are as follows:
"I was doing homework." - Ich machte die Hausaufgabe. In the third person, the forms of the verb coincide. Er (he) machte die Hausaufgabe.
A feature of the German language is also a special group of verbs, which are something in between, between the strong and the weak. So, they also acquire the suffix t in the past tense, however, the root vowel changes in preter. So these are the verbs “think” (denken). Ich denke - Ich dachte. Here e changes to a. Other verbs are as follows:
Bringen - bring (Ich bringe, however Ich brachte).
Rennen - to escape (Ich renne, but Ich rannte).
(Er) kennen - to know (accordingly - to know) (Ich (er) kenne, however Ich (er) kannte).
And also the verb nennen - call (Ich nenne - Ich nannte).
In a word, nothing complicated. The main thing is just to figure it out.