Working with IMovie os x Yosemite

I have an iMac with os x yosemite 10.10.5. I am trying to make a DVD of a movie in iMovie. I can get the movie into the timeline, but can go any farther. I have read about, watched video's, etc and nothing has helped me. Can't find my pictures for this movie in a library. I'm not sure how I got them into the timeline. I have added a transition and music to the timeline, but can't save anything. (rather don't know how). Wish I had Mountain Lion back!!