'A' and 'an' are articles used with singular nouns.
The article 'a' is used with singular nouns that do not begin with a vowel.
a motorbike
a cat
a cup of tea
a call
'an' is used with singular articles that do begin with a vowel (a, e, i, o, u)
an aeroplane
an umbrella
an orange juice
an elephant
Watch our video for an explanation of when to use the prepositions 'a' and 'an' in English.