how is an acid made?

Question

good question?

they are made from lemon juice and sour things

There must be thousands of acids and bases. And are you talking about making an acid in the lab or making it commercially. For example, HNO3, nitric acid, may be made in the lab by reacting a nitrate with H2SO4. The lower boiling point acid, in this case HNO3, will be formed and can be distilled from the mixture.
2NaNO3 + H2SO4 ==> Na2SO4 + 2HNO3

Commercially, HNO3 is made by oxidation of NH3 using a catalyst.