Layouts are one of the hardest subjects to grasp in Codename One, there is a lot of nuance in getting layouts "right". Since the subject is so vast and complex this video only scratches the surface and is still relatively long for an introductory video. It’s crucial to go thru this material though if you are not familiar with layouts or find them confusing.
Ideally, I’ll follow up with a more "pragmatic" video of layouts that will build on top of this video to explain how common layouts are achieved.
To learn more about layouts you can check out the layout gallery in the JavaDocs and dig into an individual layout. Because this is very heavily documented I didn’t add additional writeup besides the video.