Welcome tdub

You'll have to click on nectar machine, chose "add fruit" and than you'll get the same box as you get when you open treasure chest or fridge, or LN bar. Then you drag your fruit from inventory to that blue square you get, just above menu, press the "X" to close it after placing 10 fruits and then you can make nectar (and watch your Sim pressing the fruit in swimming wear).
I hope I managed to explain it good enough, let us know if you still have troubles with it.