If you want to have something happening in the background of your video while a character in your video addresses the audience in reference to the background we have a neat little trick for this. I like to call it a talking head because that's all you'll be seeing from the "narrator" character.
All you have to do is build your background scene (in my example, we have a character who's checking some flight information at the airport) and then add your desired "speaker" or "narrator" character and enlarge him to only have his/her head visible as shown below. Then, simply attach dialog if needed, lip sync no audio or even just subtitles like I did in my example!
Step 1: Build your background scene (the park in this case) and add your character. Make sure you enlarge him/her so that only the head or at most only the top part of the character's body is visible.
Once you're done adding dialog, lip sync no audio or subtitles you should have something like this as your finished product:
You can see that the main character is referencing the background scene. This is good for scenario-type videos in which you might want to help the viewer relate to the background scene and then make suggestions about that scene. In my sample GIF I address the viewer hoping they relate to the poor man who just found out the flight he rushed to is delayed (we've all been there before). Typically this main character or narrator should provide a solution or a different way of thinking about what's happening in the background.