iMovie Suggestions
Question: When I put in a transition and play the clip with the transition, it doesn't play any further, it goes to the beginning of the clip.
Possible answer:
If you have highlighted the clip and the transition, it will only play that which you have highlighted. You need to make sure that you have nothing highlighted when you click play (or hit the spacebar, which will start/stop the playing) for it to continue.
Here we have the clip and the transition highlighted. In this case, it will only play what is highlighted, and then stop. If you tell it to play again, it will play from the beginning of the clip again.

Here we don't have the clip or the transition highlighted, and have moved the playhead to before the clip starts. Now when I click Play, it will start where the playhead is and keep going until I tell it to stop.

Here is a movie which shows you what I mean. Notice that I click below the timeline to deselect the clips: