How to calculate pH and ion concentration

if the ph is 4 whats the concentration of H ions? and OH ions? and the pOH? and if the acid volume is 0.2 L how many H ions it will contain?

any help would be appreciated

pH = 4
[H+] = 10^-pH = 10^-4
so [OH-] = 10^-14/10^-4 = 10^10 [ [H+][OH-] = 10^-14 ]
0.2 L will have H+ ions = 6.022x10^23* 0.2/22.4 = 5.376 x10^21