"Nifty" refers to something that is good at what it does. A "nifty" tool does the job well. Nifty also has the connotation of being "cool," or "outside of the box."

Hi Jesús, The sentence means that a handy/stylish gadget is essential for slicing vegetables. The word has other meanings. For example, we say: 1. He is a nifty runner. (quick and agile) 2. Modern household appliances have very nifty designs. (stylish / aesthetically pleasing) 3. They came up with three nifty proposals. (excellent ideas) 4. We are pleased to announce nifty profits for this quarter. (substantial) Hope this helps. Cheers, Lance