The article “the” is the most frequently used word in English (“a/an” is the fifth). Therefore, we often assume that it should not be a problem to our students. Actually, articles are very difficult to learn for ESL students because in their own languages, they might not have “articles”.
For the definite article “the”, ESL students want to be told when “the” is used and when “the” is not to be used. Here a list I gave my students.
Where ”the” needs to be used:
1. To refer to something that has already been mentioned;
e.g. There is a watch on the table. The watch belongs to our teacher.
2. When both the speaker and listener know what is being talked about;
e.g. Remember to turn off the TV;
3. Something that is unique;
e.g. the sun, the moon.
e.g. in the east, in the south
5. Before superlatives;
e.g. the busiest day
6. Before ordinal numbers;
e.g. the first, the second, for the first time
7. With adjectives to mean a group of people;
e.g. the rich, the old
8. With names of oceans, rivers, and mountains;
e.g. the Atlantic Ocean, the Red Sea, the Amazon
9. With names of countries;
e.g. the United States, the People’s Republic of China (What we need to explain here is that “the” is used when the name of the country is composed of general English words. If the name is a proper noun which only means that country, we cannot put “the” before it. e.g. Brazil. We cannot say the Brazil.)
Readers are welcome to add more to the list.