Basic confusion about how transistors work
The sentence is talking about the voltage between two points.
It says the voltage at the base must be 0.7V higher than the voltage at the emitter. This is comparing the voltage between two points - the base and the emitter. You can measure this voltage by putting one multimeter probe at the base, and the other at the emitter, and seeing if the multimeter reads higher than 0.7V.
You could also measure the same voltage by putting one multimeter probe on the negative terminal of the battery, and the other one on the base, reading the display, then putting the second probe on the emitter, reading the display again, and then subtracting the emitter reading from the base reading. Or you could use the positive terminal. Or any other good &quot;fixed-voltage&quot; point in your circuit (an audio signal would not work because it would change in between the readings).