This article shows you where to find the advanced editing features in iMovie 10 and 11 on a Mac.
How to Enable Advanced Tools in iMovie
There is no option to show advanced tools in the iMovie 10 preferences menu. The advanced tools are located in a toolbar above the large thumbnail in the editor.
The row of icons above the large thumbnail image contains many advanced features:
You may not see all of these tools at once, depending on the type of clip you're working on.