In German, there are two different tenses we can use to talk about he past: the Simple Past Tense and the Perfect Tense.
They both mean the same thing (something happened in the past), but we use them in different circumstances (in general: the simple past when writing, the perfect when speaking).
Examples of the Simple Past Tense:
Regular verbs are conjugated by removing the "-en" ending and replacing it with another ending (based on the subject of the sentence):
If the verb stem ends in "-d" oder "-t," add an "e" before the ending.
Example with "arbeiten":
Verbs that have a vowel change are called strong verbs. These are normally the same verbs that are irregular in the present tense, but not always!
In plural, they often use the simple present endings.
In the first and third person singular, they often have no ending (the first and third person singular are always identical to each other, for both regular and irregular verbs).
Examples for irregular verbs:
About 50% of all verbs are irregular in the simple past!
Even some Germans don‘t know the conjugations of all verbs in the simple past.
When possible, they try to avoid using them. And you should to!
For completed actions in the past:
For facts and conditions about the past.
But aren't those the same times we use the perfect tense?!?!? Yep! The simple past and the perfect have the same meaning. The difference is that we use the simple past when writing (especially formal writing) and the perfect when speaking.
Rule of thumb: when speaking, if you aren't sure, use the perfect tense.
Talking about the present: The Simple Present.
When using verbs, word order is important: Main Clauses
Some verbs have to separated when you conjugate them: Separable Verbs.
Learn about modal verbs and what's so special about them: Modal Verbs.
Some verbs are always followed by a specific case: Verbs with Complements.