If we say William drives carefully we have created a sentence on the Subject-Verb-Adverbial pattern, or SVA, carefully being the Adverbial. It describes the manner in which William drives. Carefully itself is an adverb, but Adverbials do not necessarily have to be adverbs. Consider the sentence William drives too fast for his own good. The whole of the phrase too fast for his own good constitutes an Adverbial in that it too tells us something about the manner of William’s driving.
The fourth sentence structure is Subject-Verb-Complement, or SVC. At its most basic level, a Complement completes a clause or a phrase, so you might say that a Complement is anything that follows the Verb, but that would not allow us to distinguish the different ways in which a sentence can be completed. What we refer to as a Complement very often follows verbs like be and seem. These are known as copulative verbs because they join two parts of a sentence together rather in the way that an ‘equals’ sign joins together two parts of an algebraic equation. Consider the sentence William seems happy. Seems doesn’t actually tell us that William is doing anything and happy is not on the receiving end of anything he is actually doing. What we can very nearly do is replace seems with an ‘equals’ sign: William = happy. We could perhaps more readily do so if the sentence was William is happy, because is gives us a more reliable indication of William’s emotional state than seems does.