In German, there are two different tenses we can use to talk about the past: the Simple Past Tense and the Perfect Tense.
Both of them are used to express that something happened in the past and is completed. So how should we decide which one to use?
In informal language (spoken and written), we almost always use the perfect tense (there are a few exceptions, which I'll explain below). In formal writing we use the simple past.
The perfect tense is made with "haben" or "sein" (conjugated) as a helping verb and the past participle. Whether we use "haben" or "sein" depends on the main verb. Some verbs require you to use "haben," while others require "sein."
For movement/change of location (of the subject):
There must be movement from point A to point B.
For a change of condition or state (of the subject):
Note: for both of these use cases, it depends on if the subject moves / changes. If I throw a ball, the ball changes it's location but I (the subject) do not. So it doesn't fit these criteria for using "sein."
With specific verbs:
The verbs "sein," "werden," and "bleiben" always use the helping verb "sein".
We use "haben" to form the perfect for all verbs that don't use "sein."
And for ALL reflexive verbs, even if they involve a condition, status, or location change
The helping verb is conjugated and therefore goes in position 2 if it's a main clause (or position 1 for a yes/no-question). The past participle of the main verb goes at the end of the sentence.
For subordinate clauses, the conjugated verb goes last, and the past participle goes second-to-last.
For actions in the past that have been completed, we use either the perfect or the simple past. The meaning is the same, but we use them in different situations.
Written Language: For formal written language (literature, official letters, etc.), we always use the simple past.
On Facebook & other social media: When communicating with our friends and family on Facebook or other social media, we use the perfect tense, because it's kind of like having a conversation.
There are some regional differences with their use as well. In general, the farther north you go, the more the simple past is used. But even in the north, that's changing - they are using the perfect tense more and more.
And in Swiss German, the simple past doesn't even exist! But don't try avoiding the simple past completely - it's possible to use modal verbs and subordinate clauses in the perfect tense, but it's super difficult and confusing!
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.