Some food is unsuitable for chopping/slicing/grating. Ensure you are using the correct cone/cassette for the food you are trying to prepare and that the food is positioned in the correct position first in the feed tube before slicing/grating/chopping. Also the ingredients you use must be firm and fresh quality to get satisfactory results and avoid accumulation of food in the holder (information will depend on model of product).
If pieces of food get stuck to the side of the bowl (ham, onions, etc.), switch off the appliance, take out the plug, remove the pieces with the help of a spatula, and re-distribute them in the bowl. Plug the appliance in again and pulse 2 or 3 times more. NEVER put your fingers or hands in the bowl, or near the blade.