Most German sentences contain at least one conjugated verb and one component in the nominative - a subject. There may also be other components that accompany the verbs, such as objects.

Adverbials are words or groups of words that provide more information about the circumstances surrounding the action or condition described in the sentence. Adverbials can relate to location, time, manner or reason.

Compulsory and non-compulsory adverbials
Adverbials can be compulsory components or non-compulsory additions in a German sentence. That depends on the predicate (conjugated verb + (if present) the participle/infinitive, etc.). If the verb requires an object, then that's known as a compulsory component. Without it, the sentence would make no sense. Non-compulsory adverbials can be omitted. They provide additional information.