The salt goes in the salt compartment in the base of the dishwasher. Open the door and pull the lower basket out. You should then be able to see a cap near the front-left corner of the base of the dishwasher. Unscrew this cap (anti-clockwise) and fill the compartment with salt all the way to the top - or with as much salt as you have in the packet - then screw the cap back on firmly, but do not over-tighten it. The salt compartment will (or should!) be full of water and some will spill out as you fill it with salt. This is totally normal and not indicative of any problem.
Do not use any type of salt which is not sold specifically for dishwashers. The dishwasher can be used without salt but it is not advised and may result in a white film being left on your cutlery, glassware and/or dishes.
It may also be possible to provide a user manual in PDF format which you can download, but I would need to know the model number. If you don't know the model number Most Neff/Bosch dishwashers have the model number laser-etched into the stainless-steel at the top of the inner-door or the rim of the washing compartment. Please click on the link below for a guide to locating the model number of your dishwasher. (Neff is a Bosch owned brand)
Hope this helps. Please let me know if you would like the manual or need further assistance.