The indefinite article a/an is used:
• with
singular countable nouns when we talk about them in general. /
need a
new
handbag.
• with
the verbs to be and have (got). Jane
has (got) a
cat.
It's a
Siamese.
• before
Mr/Mrs/Miss/Ms when we refer to an unknown person. A
Mr Wells is waiting for you.
• to
show price in relation to weight.
The
tomatoes cost one pound twenty a
kilo.
• to
show distance in relation to time. My
car can go 250km an
hour.
• to
show frequency.
/
work
at the library three days a
week.
We
do not use a/an:
• with
uncountable nouns or plural countable nouns. We use some
instead
of a/an.
We
bought some
chocolate and
some
walnuts.
This
dress is well-made.
But:
This
is a
well-made
dress.