How does length of resistor affect the value of resistance?
Since you cannot measure resistance directly, you will need to measure current (using your multimeter) and then calculate resistance using V=IR. Remember, your goal in this lab is to measure the relationship between length and resistance. These are the two variables that should be in your graph and data table. What you will be actually measuring in the lab is length and current. Once you write down the value of current in each measurement, a group member should immediately calculate resistance, since that's what you actually want.
Change the length of the resistor (pencil lead) by breaking the lead little by little. Make sure to measure the length each time you break it, and always have your two leads connected to the very ends of the lead. If you don't, the length you wrote down will not actually be the length you used.