Electric Heater Design
Yes, it's that simple. Of course, if you make poor choices, you can also create a smoke, light and/or sound generator (single operation for those, usually.)

The vast majority of electric heaters are operated from fixed voltages at fixed power. Naturally, if you choose a resistor with inadequate power rating, it will tend to the smoke generator end of the spectrum.

A typical 500W at 240VAC baseboard heater will be about 115 ohms. The larger size of standard electric cookstove elements is about 25 ohms.

Control in most applications is full on or full off. Something like an electric stove control does not "turn down the voltage" - it adjusts how much time the burner is on .vs. how much time it's off. That can be done at very high speeds to get fairly precise control.