Assuming the heating element is a pure resistor, the power drawn will be defined by the voltage of the source (220V in your case), and the resistance of the heating element. The power can be calculated as the product of voltage and current, and the current can be computed using Ohm's law:
$$P = I \times V = \frac{V}{R} \times V = \frac{V^2}{R}$$
A space heater might have a 30 ohm heating element. When connected to a 220V supply, this would result in
$$\frac{(220V)^2}{30 Ω} \approx 1613W$$
As for your additional question, there are a couple common ways of controlling this power.
A cheap space heater might simply have two heating elements of different resistances, and a switch allowing you to connect power to just the low-power element, just the high-power element, or both elements, giving you four (including off) power settings.
Another method, commonly used in stovetops, is to turn the heating element on and off with a given duty-cycle. If the element is outputting 1 kW, 70% of the time, and is off the other 30% of the time, the average power output will be 700W. In these applications the thermal load will normally be high enough to smooth out the fluctuations, so that the switching on and off can be done quite slowly (several seconds between switchings).
