One cup contains 8 ounces.
There are 8 ounces in a liquid measuring cup.
So there are 8 ounces in a cup.
Of course that can depend on the size of the cup you have because some cups come in different sizes but for the average size cup there are 8 ounces in each of those cups.
When doing any baking or cooking it's best to use measuring cups instead of a regular cup to make sure you're getting the correct amount of ingredients.
In some recipes adding too much of an ingredient or too little of an ingredient can make the recipe turn out bad.
The measuring cups will list the ounces that are in the cup so that you get the correct amount of ounces you need.