Banana’s work wonderfully to propagate plants (in other words,you can grow multiple plants from existing plants, potentially saving you hundreds of dollars in landscaping expenses.
As you can see from the video, the person basically stuck a lemon cutting into half of a banana (with the peel), placed it into a potting mix and perlite combination, watered it, and within 25 days (according to the video), the cutting had roots.
How to Root Plants using a Banana
https://www.youtube.com/watch?t=6&v=s4jtwX-7MFI&feature=youtu.be
The trick to successfully rooting a plant is to ensure that you prepare the cutting properly. Start by taking a non-flowering, green-wood stem cut at the base at least 2″ below a leaf/node pair. Trim the leaves by cutting them in half.

Leave between 1 and 2 inches below the leaves for sticking into the banana.
See also, How to Root Hydrangeas from Leaves.