how is an acid made?

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.

To clarify, acids can be made in different ways depending on the specific acid and the purpose for which it is being made.

In general, acids can be synthesized through chemical reactions involving certain compounds or elements. One common method for producing acids in the laboratory is by combining a metal or non-metal oxide with water. For example, sulfur dioxide gas (SO2) can react with water (H2O) to form sulfuric acid (H2SO4) through the following reaction:

SO2 + H2O → H2SO4

Another common method for making acids is through the reaction of a non-metallic oxide with a basic substance. For instance, carbon dioxide (CO2) can react with water to form carbonic acid (H2CO3) through the following reaction:

CO2 + H2O → H2CO3

In commercial production, acids are often manufactured on a larger scale using more complex processes. For instance, nitric acid (HNO3) can be produced commercially by oxidizing ammonia gas (NH3) with a catalyst such as platinum or rhodium, resulting in the formation of nitric acid and water:

4NH3 + 5O2 → 4NO + 6H2O
2NO + O2 → 2NO2
2NO2 + H2O → HNO3 + HNO2

These are just a few examples of how acids can be made. Remember, there are many different types of acids, each with their own specific methods of production. So, the process may vary depending on the specific acid being made.