We have two articles in English. They are a and the.
We use a with countable singular nouns. We use a when we tell somebody about something which only we know.
We use the with all nouns. We use the when we speak with somebody about something which we both know.
There are words that push out articles. These words are numbers, pronouns my, your, his, her, its, our, their, this, that, these, those and the words every, some and any.
I am in a new situation. The situation is bad. I work for the captain. I work in the garden. I don’t like my work.
You can see more examples in the book Robinson Crusoe.