In Lecture 4, students learned about articles in English grammar, including the definite article “the” and the indefinite articles “a” and “an.” They studied when to use “the” for specific things, unique objects, groups, superlatives, rivers, oceans, mountains, and some countries, and when not to use it for general ideas, names, cities, and languages. They also practiced the correct use of “a” before consonant sounds and “an” before vowel sounds. Exercises from the book helped reinforce the correct usage of articles through fill-in-the-blanks, rewriting sentences, and choosing the correct forms.