Lego Technic Servo Motor - 9V PWM
Yes, the output will be a pwm. You can see it from the schematics.
you have few options, with different precision and complexity:


Configure one of the PWM HW blocks
Do it by sw in a loop
Use a timer to trigger a sw function - but it might be simpler to just configure the PWM HW block.
Use some existing library that will implement one of the methods I listed



I would recommend Option 1: it's not so difficult, you will learn something of the AVR internals and it will be the solution with the least overhead. You can have a look at this tutorial. There are also many others floating around.