Understanding the properties of acidity would be a valuable tool to support estimations of how two substances will react. It would also be useful in real life, where you can use bases like antacid to neutralize stomach acids if it is inflicting pain. Lets see how we can determine wether a substance is acid or base:
*As a matter of fact, there are many opinions from various scientists to determine acids and bases so I am just going to use the Bronsted-Lowry method to keep thinigs simple.*
In the Bronsted-Lowry definition, an acid is anything that is willing to "donate" a proton (Plus one charged Hydrogen atom) and a base is anything that accepts a proton.
For example here is a Lewis structure of Propanoic acid:
Here is water:
If we put the propanoic acid into water, the water will act as a base and "Grab" the Hydrogen atom (On the right side of the picture of propanoic acid) and forms a hydronium ion. It will also have a positive charge due to the extra proton.