Adverbials are adverbs, adverbial phrases or adverbial clauses which give us additional information about the time, place, or manner of the action described in the rest of the sentence.

I had been reading my book quite happily on the sofa for half an hour, when my little brother burst into the lounge with his skates on.

The most common position for adverbials is at the end of the sentence. If there is more than one adverbial then place adverbials (on the sofa) come before time adverbials (for half an hour) and manner adverbials (quite happily) come before place adverbials (on the sofa).

However this is not a strict rule and you can, for example, start a sentence with an adverbial clause if it helps highlight something in particular.

When the lightning struck our house, we were sleeping peacefully in our beds.

Useful Links

Adverbs‏‎ in English Grammar – all about the different types of adverbs and their position in a sentence

Adverbial Phrases‏‎ in English  – explanation with examples of what these phrases are and how they work