Every tutorial I've found on the internet connects the oscillator in and the oscillator out with a resistor. What can these ports be used for?
There is an internal RC oscillator (the capacitor is inside, and connected to OSC1). The external resistor forms part of the oscillator.
see the datasheet: http://www.holtek.com/pdf/consumer/2_12ev120.pdf Page 9 gives the oscillator frequency vs. the resistor value.