In other words: if a voltage of 10V DC heats a resistor from freezing point to a hundred degrees, the exact same thing will happen if you apply 10V AC (eff).
Unfortunately though, it is not easy to measure this. There exist very expensive instruments that basically measure the heating effect that a voltage has and thereby provide an accurate AC voltage value. Those will certainly not be available in an amateur environment.
How regular multimeters work in comparison to this is by measuring the PEAK AC voltage of the applied waveform (the highest voltage that the waveform reaches) and from that they calculate the effective voltage. Unfortunately again, that is not trivial. For a completely clean sine wave, both voltages would be related by the factor 1.414 (root of 2).
For other wave forms this factor differs, for completely random waveforms, the factor is not predictable.
This is why cheap AC voltmeters can only provide accurate readings for sine-shaped waveforms. More expensive voltmeters can to a degree provide measurements for other waveforms too (called RMS voltmeters) but even there limitations exist as to for what frequencies this can be accomplished (usually 50Hz only).
