The document discusses the differences between using gerunds and infinitives in English sentences. Gerunds can be used as subjects and objects, and after prepositions. Infinitives are used after modal verbs and in structures like "to be + adjective + to + infinitive". Certain verbs like "want" and "intend" are usually followed by infinitives, while verbs like "remember" and "forget" can be used with either gerunds or infinitives but with different meanings.