There are two kinds of articles: the definite article (equivalent to “the”) and the indefinite article (equivalent to “a, an”). Articles must follow the noun’s gender, number and case (the noun’s function in a sentence). 

Τip:  Study the articles together with nouns. You will learn them faster and you may also remember the cases more easily.

The definite article is used for:

• something known to the people who have the conversation
• a fact or a general remark
• something that is unique or represents its kind 
• quantity
• non-nouns that are changed into nouns e.g. “the how”
• time, in a specific way

Το φαγητό είναι έτοιμο. (The food is ready.)
Ο ήλιος ανατέλλει κάθε πρωί. (The sun rises every morning.)
Τα τριαντάφυλλα είναι κόκκινα. (Roses are red.)
Κοστίζει τρία ευρώ το κιλό. (It costs 3 euros per kilo.)
Θέλαμε να μάθουμε το γιατί. (We wanted to know the why.)
Θα πάω σήμερα το απόγευμα. (I will go this afternoon.)

The indefinite article is used for:

• something known to only one or some of the speakers
• something that is introduced in the conversation and will take a definite article afterwards
• something that doesn’t exist yet but may do in the future  
• time, in a fluid way

Μόλις ήρθε ένας φίλος μου. (A friend of mine just arrived.)
Συνάντησα μια ηλικιωμένη κυρία. Η κυρία… (I met an old lady. The old lady…)
Θα ζωγραφίσω μια γάτα. (I’ll draw a cat.)
Κάποια μέρα θα ταξιδέψω. (Some day, I will travel.)

When not to use articles:

• when we describe characteristics and features (e.g. professions, appearance)
• when we provide general information about specific people or circumstances
• when the meaning of the verb is incomplete without the noun
• when using noun+noun and noun + adjectival noun expressions 
• when we talk about materials
• when we talk about content
• when we need to express a negative meaning.
• in similes  

Η Άννα είναι γιατρός. (Anna is a doctor.)
Το κουτάβι μου έχει καστανά μάτια. (My puppy has brown eyes.)
Ζουν σε διαμέρισμα. (They live in a flat.)
Πίνουμε τσάι. (We are drinking tea.)
Κάνουν θόρυβο. (They make noise.)
Αγόρασα παπούτσια χορού. (I bought shoes for dancing.)
Μια καρέκλα από ξύλο. (A chair made of wood.)
Ένα ποτήρι νερό. (A glass of water.)
Δεν ήταν κανείς εκεί. Ούτε ψυχή. (There was no one around. Not a soul.)
Πεινάω σαν λύκος. (Hungry like a wolf.)

Don’t forget to put articles in front of proper names!

Είμαι η Χριστίνα. (I am Christina.)
Ο Καναδάς είναι μακριά. (Canada is far.)
Το Παρίσι είναι μεγάλο. (Paris is big.)