1/2 cup of spinach is "one-half cup" of spinach
1/3 is "one-third"
But what do you say for 3/4 and 3/5?
You say "three quarters of a cup" or "three fifths of a cup". In US English you sometimes come across "fourths" instead of "quarters" but that is unusual elsewhere.
It would also be more natural to say, for example, "half a cup of spinach", rather than "one half-cup of spinach".
For other fractions with numerator 1, you would usually say "a third of a cup", "a quarter of a cup", etc.
All these numbers are fractions, which is the answer to the title of your question. The examples you use suggest that you actually want to know how to pronounce these fractions.
In addition to the correct answer by user3724662, let me mention that an expression such as "2/x" is pronounced as "two over x". The use of "over" may also be simpler once the numbers involved become very large (compare "eleven over ninetynine" with "eleven ninetynineths").