Tap the green (+) button Tap CALCULATOR to open it

The calculator will ask for the nutritional data that is relevant to the plan you are on.

You can use this screen to just figure out the BITES of any food item or you can permanently 

Create it as an item on the next screen.

If you want to TRACK the food after calculating - it will ask you for more information on the next screen. If you are wanting to track calories or macros as a secondary metric - you need to fill in ALL the details.