You just need to know that pH is the logarithm of the inverse of the concentration of hydrogen ion.
Mathematically this is: pH = log { 1/[H+] }
Then if you know the pH you can find [H+] using the properties of the logarithm function.
=> pH = - log [H+] => [H+] = 10^(-pH)
=> [H+] = 10 ^(-8.25) = 5.62 * 10^-9
Answer: the concentration of hydrogen ion, [H+], is 5.62 * 10^-9 M
