A short at the far end will invert the reflection. The time displayed is twice the cable length, since the signal goes through the cable twice, to the far end and back to the oscilloscope. Since the termination isn't perfect, you can see secondary reflections trailing away to the right on the scope's display. Commercial TDR units are often calibrated in footage or meters so you don't need to do a conversion from time to distance. This brings up the topic of cable propagation delay.
Signals travel through cables at a percentage of the speed of light.
Different cables have different propagation delays. Impulse type TDR is a somewhat crude, brute-force method useful mainly for cable length measurements and for locating gross fault conditions like a severed cable, a dead short, or a really bad kink. The step-voltage system allows measurent of the impedance of the cable, any connectors or splices, and the termination at the end. The amplitude of the voltage reflection is related to the impedance of the cable at any given point. The flat-line portion on the scope's display is the characteristic impedance of the cable, say 50 or 75 ohms.