Concentration and pH help

Hi, i'm really confused what to do when compounds like H2SO4 and Ca(OH)2 are used in pH and buffer questions.

How would I determine pH of a solution that has e.g. 0.3moldm-3 conc of h2so4

What do i have to do to the moles of h2so4 and ca(oh)2 in buffer questions e.g. h2so4 reacting with naoh and hcl reacting with ca(oh)2

if i'm told the ph is 1.2 in solution of h2so4 how would i determine the moles/conc of the h2so4

etc

Any help on this is greatly appreciated, thanks in advance!

If you have 0.3moldm-3 H2SO4 and this dissociates fully, you'd have 0.6moldm-3 of H+ (stoichiometry). Other than that, the same rules apply as with any other acid.
Ca(OH)2 would have 2 x the concentration of OH- ions (you can work it out as pH=14-pOH).
If the pH is 1.2, you can do 10^-pH to get the H+ concentration. You know that there are 2x H+ for every 1 H2SO4 therefore divide the [H+] by 2 to get the [H2SO4].
Hope this helps