Select File > Info.
Select the Check for Issues button.

On the Insert tab, in the Illustrations group, click 3D Models > From a File.

Navigate to where your 3D object is, select it and click Insert. Once inserted and still selected, you will see some handles with which to manipulate the object.

These handles look like the usual ones that allow you to resize and rotate an object. However, if you hover your mouse roughly over the centre of the object, you should see the cursor change shape to indicate that you can rotate the model in 3D space. Like this:

Once you have rotated the model, the 3D rotate handle will appear in the centre of the object and using this will make it easier to rotate the object.
While the object is selected, you will see the 3D Model Tools contextual tab displayed in the ribbon.