pH is a measure of the concentration of hydrogen ions in a solution. Strong acids like hydrochloric acid at the sort of concentrations you normally use in the lab have a pH around 0 to 1. The lower the pH, the higher the concentration of hydrogen ions in the solution.
The greater the value of Ka (dissociation constant), the more the formation of H+ is favored, and the lower the pH of the solution. Similarly, lower the value of Ka (dissociation constant), less the formation of H+ is favored and higher the pH of solution.
Stronger acids have a larger Ka and a more negative pKa than weaker acids.
Strong acids are: H2SO4, H3PO4 , HCl, HNO3 etc.
Strong bases are : NaOH, KOH, LiOH etc
If pH is between 0 - 2 solution is a strong acid
If pH is between 12 - 14 solution is a strong base