Dogzilla, Anaamika,
I don’t have your particular model of mandoline. I do, however, have a Matfer mandoline that looks similar. (and gave me similar fits when I tried to figure out how the hell it worked.) Looking at the nine photos on the Amazon page, combined with my slicer, I think I can help you both with how to use the bloody thing.
First, I recommend Very Strongly that you always use the food holder, as well as a cut-resistant glove when using the device. You will cut your hand open if you omit either of those steps. Just trust me on this.
Second, looking at your device, and imagining it set up on the table, with the upper end at the left and the lower end on the right, I notice a knob higher up than the slots you stick blades in. This knob raises and lowers the upper, hinged plane in order to vary the slice thickness. On mine, the lower plane is removable and screws into the mandoline. On one end of the plane is a straight razor blade, the other end has a waffle cut side.
Yours looks like it’s a bit different. Lower down the mandoline is an L-shaped slot, with the long axis of the L parallel to the upper plane, and the short axis of the L higher up the mandoline. From what I see, the long axis is for placing the flat, long blades, like the slicer, the grater(s), or the waffle cutter. As you note, they only go in one way. To use, put on your cut-resistent glove and place whatever you want cut on the spikes of the food holder. Then use your gloved hand to slide the food holder and thing to be cut down the slope of the upper plane until you reach the bottom. The slicer, grater or waffle cutter will be sticking up a tiny bit, and will easily slice a bit off the bottom of whatever’s attached to the food holder. It gets easy with practice, anyway. The slice on mine falls underneath the mandoline. I don’t know whether on yours it falls within a catcher or not. Turn the knob to vary how thick you want things. It looks like on yours that to use the grater, you might need to raise the upper plane all the way to the top
You’ll note that the julienne blades look like a row of metal right triangles. You want the hypotenuse of those triangles to be upslope from the long side of the right triangle. It does not look like the mandoline requires that you also have one of the flat long blades within the device at the same time. It does look like that you can use the julienne blade with any of the flat long blades. Does the julienne blade look like it locks into the mandoline somehow? Mine relies on friction between two raised ends of the sides of the julienne blades against similarly raised areas within the slot.
So, after all this effort, what do you get? It allows me to crank out see-through cucumber slices as fast as I can whip a cucumber up and down the ramp. It’s the only way I can make zuchinni noodles (with the julienne blades) without losing my mind. And it will whip out waffle cut patty pans with amazing speed. Balance that against it being a PITA to clean.
Sorry about the length. Feel free to bombard me with questions; I’ll try to help.
Edit: It pays to quick review first. Congrats on the video.