unable to add titles to iMovie event

You need to create a Project first. Then drag clips (or parts of clips) to the Project. You can then do all of your editing, including adding titles, in the Project.

See this Apple Help article for how to start a new project:

http://help.apple.com/imovie/#mova719fa33

And this one for adding video to your project:

http://help.apple.com/imovie/#mova719fd26

NOTE: Be sure to watch the 2 video tutorials included in the articles.

John