Import your animated box (We looked how to create this here). If you havn't made your own you can import our downloadable asset. Select the imported fbx file in the project window to bring up it's setting in the Inspector Window.
Now select the Animations tab so we can split the animations contained within the fbx file into an idle animation and an open animation.
You will notice that we currently have one animation which lasts 36 frames. If you press play at the bottom of the inspector window it will show the full animation playing.
We now need to split the animations up so that we have two animations we can use in the Machanim Animator in the next step. This is done by slecting and editing the name of the animation, here we have called it IDLE_BOX and changed the end frame to 12.
To create the second animation click on the plus icon below our IDLE_BOX animation and name thios one OPEN_BOX , select the start frame to be 13 and the end frame to be 36. Click apply.
You can check that it has worked by opening up the box asset in the project window, and it will have two animation assets we can use.