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I understand German has separable verbs and normal verbs for some actions
For example:
and lot more..
When to use the separable and when to use normal verb? Is there any hard and fast rule to use the separable and normal at specific places?
No, there is no rule that requires you to differentiate in use. Your examples are mostly interchangeable. There are some subtle differences in meaning, particularly stornieren and absagen, but that has nothing to do with the fact that they are separable or not
Your question has already been answered, but let's make the point more generally: A language learner's perspective on a language will be completely different from a native speaker's. The learner's attention will always be focused on grammatical properties of lexemes: separable or non-separable verb, strong or weak declension, strong or weak preterite, etc.
Wann fangen die Ferien an? – Wann beginnen die Ferien?
der Insasse, den Insassen – der Häftling, den Häftling-∅
tragen, trug – schleppen, schleppte
They need to do so in order to pick up the grammar (unless they are children and can learn by immersion alone).
But native speakers are usually completely oblivious to the grammatical properties of lexemes, unless they have been taught to pay attention. (And paying attention to the structure of language can become a hobby, which is when you join Stack Exchange…) It follows that usage is independent of a lexeme's grammatical properties: Non-separable verbs are not used in other contexts than separable ones.
By grammatical properties I in this case specifically mean oppositions between lexemes, as illustrated by the examples, and not oppositions between word forms or grammatical categories such as trägt (present) vs. trug (past).
In addition to @PiedPiper's answer. The separable verbs are mostly based on very general verbs:
While they are quite commonly used in german, there are some downsides. A general verb can be used in various contexts, making it generic or even an indication of a very limited vocabulary. There might be examples where using the more fitting verb for the context is considered better style.
e.g.
Er machte seine Schnürsenkel zu.
He "closed" his shoe laces.
Er schnürte/band seine Schnürsenkel.
He tied his shoe laces.
Ihm sagte die Atmosphäre zu.
He did like the atmosphere.
Er genoß die Atmosphäre.
He enjoyed the atmosphere.
