iMovie 10.0.6 for Yosemite help needed
I wouldn't say it's for no rhyme or reason, obviously,things sorted chronologically will always be easier to find. But this is just a slight overlook on your part, very slight. You can create a new project with the following:


clicking on the 'Add' icon in the topbar or pressing ⌘+N.
Create with whatever theme you seem fit.
Name it whatever suits you, and select the corresponding event your creating a movie from.
This will automatically add the project to the same year or folder the event is in (keeping things together, more efficient workflow)
You know if an event has a working project if there is a movie slate next to it's name. 





Is a fast link to your movie.
This is where you cut/exclude/split and select certain clips to drag-n-drop into the timeline (#3)
This is your working timeline, anything you've added to the movie will display here. All transitions go here as well.
Self-explanitory


This is a very very fundamental tutorial, there are thousands of features packed into iMovies you might have to review their own tutorials here : http://help.apple.com/imovie/mac/10.0.6/