Depending on the food you are mixing and the jar you are using, the mixing process will vary, and food might get stuck. There is a learning process to the device, and with time you will learn what works well and what doesn't.
Here are a couple of tips if food gets stuck:
Take the jar and blades from the mixer and shake it downwards, while the jar with the blades is still closed.
Open the heads from the jar and scrape it off
Add some more water or oil
Use a jar with straight vertical walls such as this one. This allows the food to fall down more quickly, and keeps it closer to the blades. This is especially useful for sticky stuff like the choco spread