The lesson focused on measuring the resistance of a lamp using a voltmeter and an ammeter. The instructor explained that the voltmeter should be connected in parallel while the ammeter should be connected in series with the lamp in the circuit. By taking readings of voltage and current, students can use the formula for resistance (R = V/I) to calculate the resistance of the lamp. The lesson also covered how varying the current and voltage affects resistance and emphasized the relationship between voltage and current as directly proportional at constant temperature, which can be graphically represented.