How Many Grams Of HCL Are Needed To Prepare 500 Ml Of A Solution With PH = 3.0?

To convert pH into concentration, you need to pres shift ->log ->- and then number 3.0. This will be shown as ₁₀-3.0 in your calculator.

[H⁺] = ₁₀-3.0
[H⁺] = 0.001 moldm^-3

As, HCl is a monoprotic acid, 1 mole of acid will give 1 mole of [H^+]  ions in solution, so its concentration will also be
0.001moldm^-3

n = C * V
n = 0.001 * 500/1000   (as 500 ml = 500 cm3 = 500/1000 gives value in dm³)
n = 0.0005 moles

Moles = Mass/Mr
Mass = Moles * Mr
         = 0.0005 * 36.5
         = 0.01825 g = 0.018 g