wahr
true
Corresponding to the facts or reality; correct and not false.
Die Geschichte, die er erzählt hat, ist tatsächlich wahr.
The story he told is actually true.

true
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true
Corresponding to the facts or reality; correct and not false.
Die Geschichte, die er erzählt hat, ist tatsächlich wahr.
The story he told is actually true.

The adjective 'wahr' (true) is the core of a word family. Derived from it are, for example, 'die Wahrheit' (the truth, noun), 'wahrscheinlich' (probably, adverb, 'presumably true'), and 'bewahrheiten' (to prove true, verb, 'to turn out to be true').
Niemand kennt die ganze Wahrheit.
No one knows the whole truth.
The expression 'nicht wahr?' (isn't it?/right?) is a fixed question that you put at the end of a sentence to ask for the other person's agreement. It always stays the same, no matter how the main clause is structured.
Du kommst morgen auch zur Party, nicht wahr?
You're coming to the party tomorrow too, aren't you?
The expression 'etwas wahr machen' (to make something come true) means to turn a wish, a dream, or even a threat into reality. The object stands between 'wahr' and 'machen'.
Sie hat ihren Traum wahr gemacht und ein eigenes Café eröffnet.
She made her dream come true and opened her own café.
When 'wahr' (true) stands alone as a predicate, it usually means 'correct'. When it appears declined before a noun (e.g. 'ein wahrer Freund' — a true friend), it often means 'real' or 'sincere'.
Ist es wahr, dass der Zug ausfällt?
Is it true that the train is canceled?
or
'oder?' and 'nicht wahr?' can both appear at the end of a sentence when you are looking for confirmation. With 'oder?', the question often sounds everyday and direct: you are not completely sure or want agreement. 'nicht wahr?' has the same function, but sounds a little more formal or explanatory. They can be confused because both turn a statement into a follow-up question. The important point is: 'wahr' on its own normally means 'correct' or 'real'; in this relation, we are only talking about the expression 'nicht wahr?' at the end of a sentence.

Du kommst morgen auch zum Training, nicht wahr?
You’re coming to training tomorrow too, aren’t you?
Der Kurs beginnt heute um neun, oder?
The course starts at nine today, right?