In English, what is an expression? What about adverbials? (preferably with easy-to-understand answers)

Predicates describe "what" or "how" the subject is. It is generally served by nouns, adjectives, adverbs, prepositions, and infinitives, that is, words or phrases equivalent to nouns or adjectives.

For example: She is always so graceful. (graceful is the slogan)

I am a teacher. (teacher is the slogan)

They are at home now. (at home is a slogan)

Adverbials are used to modify verbs, adjectives or adverbs. It generally expresses the time, place, purpose, manner, degree and other meanings of the behavior. It is often expressed by adverbs, prepositional phrases, infinitives or words or phrases equivalent to adverbs.

For example: He did it carefully. (carefully is an adverbial)

They will be arriving here tomorrow. (here tommorrow is an adverbial)

Last week, I went to the theater (Last week and to the theater are adverbials)