Check the transmission fluid level with the dipstick at the rear of the engine on the right side. If you have no fluid, add some and see if it is leaking out and where. It could possibly be the transmission cooling lines at the bottom of the radiator leaking. If the fluid has all leaked out, fix the leak and refill it and see if the car will drive. It sounds like the fluid all leaked out and the transmission will not work without it. It is possible that if you fix the leak and fill it it could work. It is hard to diagnose with what little info you have given. Try adding fluid and see what happens. You add the fluid through the dipstick hole with a small funnel. You must use "hospital" clean techniques when dealing with the transmission. In the manual Mercedes claims you should wipe the dipstick with a clean piece of leather to avoid getting lint from a rag into the system. So, get a clean funnel and something lint free to wipe the dipstick, I use my fingers and wipe my fingers on the rag. You check the fluid with the car running in neutral at idle and hot. Use a high quality transmission fluid, synthetic is my choice. You will probably want to drain the transmission and replace the filter at some point. This is another whole job. For now, find and fix the leak and fill the tranny and go from there. Don't keep trying to get it to move until you have enough fluid in it, you can damage the transmission, if it isn't already.
You also could just have a bad shift linkage bushing. If your shifter just "flops" around and feels ineffective it could be the little nylon bushings, one on the shifter and one on the transmission under the car. Search on this sight for "linkage bushing" or "shift linkage" you will probably find tons of stuff as this has been covered plenty of times. Just about every W113 made by now either needs them replaced or has had them replaced.
You should go through the whole car and check all of your fluids, get out the owners manual and read the whole book, cover to cover. You will learn many things about your car in the manual. It is very detailed. There is a separate manual covering the automatic transmission.