Buffer solutions are Weak acids or bases, which when adding acids or bases, change from or to the conjugates, eliminating the strong ions, making it require a lot more additional solutes to raise/lower the pH.
NaC2H3O2? → Na+ + C2H3O2-
HC2H3O2 ↔ H+ and C2H3O2-
With excess H+, the protons are added as such, to the solution.
H+ + C2H3O2- → (miniscule ← ) HC2H3O2
Conjugates of Weak Acids and Weak Bases; i.e. { C2H3O2- and NH4+ } can absorb H+. and OH-. Respectively. This makes saline solutions that leave Conjugates very stabile at pHs because they are constantly maintained by the equilibrium of the WA and WB.
Buffers are everywhere. In our blood, CO2 and H+ ↔ HCO3+ and H+ ↔ H2CO3 helps to maintain pH balance of one of the most critical parts of our bodies.