Usually you would rather import the whole project, including the configuration of the datasets used by the notebook. For instance, for our trainings, we have a project with a few toy datasets and a few Python notebooks playing with them.
But if you have a few .ipynb files and need to import them, it is enough to put them in the directory DATA_DIR/config/ipython_notebooks/PROJECT_KEY/.
From inside a project, choose Notebooks (G+N), + New Notebook -> Python (or open an existing Python notebook). From the Jupyter Notebook, choose File -> Open and then option to Upload on the top right of the new view.