A little help please :)

Hello,

I'm just new to Creo and I'm training with it. It's may stupid but I have difficult with "side milling" I don't know how to mill this part. When I choose a side milling tool, and select that volume, it said that the cut path could not be created...and I can't find any tutorial bout this situation

Can you show me some simple step bout this

Thank you for reanding and sorry for my English.

Have a nice day