The definite article is used to identify a specific noun or to refer to a noun that has already been mentioned. (This is similar to English)

Before general concepts or truths (English usually does not use an article in this situation). 

With dates: 

For days of the week and repeated moments (mornings, afternoons, evenings, nights…): 

With body parts (most of the time): Note that English can be different. 

To express likes and dislikes:  With verbs of preference: aimer, adorer, préférer, détester.

Note: English does not use an article in this situation. 

Use the indefinite article to talk about things that are not specific.  

In English, you would use “a” or “an.” 

In the plural, the indefinite article (des) is always necessary.  

In the negative, un, une, des ⇒ de, except after the verb être.  

In English, this is sometimes expressed with “not any”. 

With professions (student, nurse, mathematician), religion, and nationality, there is no article. 

Note: English does use an article in some of these situations.