GILLES Sebastien
--- a/HandsOn/HowTo.ipynb
+++ b/HandsOn/HowTo.ipynb
   ]
  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Declaration and definition"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "We saw briefly [here](http://localhost:8888/lab/tree/1-ProceduralProgramming/4-Functions.ipynb#Function-declaration) and [there](http://localhost:8888/lab/tree/1-ProceduralProgramming/4-Functions.ipynb#Function-definition) what is the difference between the declaration and the definition of a function (and also from other stuff such as objects that we'll see in part 3).\n",
+    "\n",
+    "We'll explain in a [late notebook](http://localhost:8888/lab/tree/6-InRealEnvironment/2-FileStructure.ipynb) how to properly structure a project with several files, but for the hands-on the idea is not to bother with this and each exercise is fully present in one file (see above).\n",