This is all about identifying the category of each word on a sentence
First you wanna review the parts of speech. Understanding what nouns, pronouns, verbs, adjectives, conjunctions, prepositions, etc. are is essential to sentence diagramming.
Then find your subject and your verb.
Here below you can see your two verbs, adverb, subject and noun.
Mr.Carrington collects aluminum can and returns them for recycling.
Subject is italicized, verbs are bold, nouns underlined, and adverbs is bold and underlined. Hope this helps!