a (an), the, -

- use (-) with plural and uncontable nouns when you are talking about things in general
- use a/an - with singular contable nouns when you are not talking about a particular thing, or when you mention something for the first time
- use the - with any type of noun when you and your reader/listener know which particular thing you are talking about, for example because it is unique or it has been mentioned before
- use the - with a singular contable noun or an adjective to talk about things in general
- use (-) - with most place names
- use the - in fixed phrases such as in .... 1960s, in ... beginning


indefinite article (a/an) 

- when it's not clear (or important) which one is being talked about
- when it is the first time something is mentioned
- in phrases of quantity of frequency

no article
- to talk about things in general
- for most continents, countries, towns, roads, stations, individual mountains and lakes

definite article (the) 
- when it's clear what is being talked about
- when something is unique 
- when something has been mentioned before
- + adjective or singular countable noun to talk about things in general
- for oceans, rivers, groups of islands/regions, deserts, mountain ranges, decades