The document discusses finite and non-finite verbs. A finite verb is one that can show tense, while a non-finite verb cannot show tense. Examples of finite verbs are go, went, and do. Examples of non-finite verbs are to go, done, and going. For a clause to be a main clause, it must have a subject and finite verb. Phrases do not have subjects or finite verbs.
It also discusses main clauses and subordinate clauses. A main clause can stand alone as a sentence, having a subject and verb. A subordinate clause depends on the main clause for its meaning and cannot stand alone, though it also has a subject