Creating collections is the first step to creating a playlist. But you can take your collections to a new level by customizing your playlist to play in the order you like. uvLayer plays the videos from top to bottom, if you're in stacked view, or they play from the upper left to the bottom right in the window view. There are a few different ways to accomplish this.
If your collection is in the expanded window view, drag and drop each video to the new location.
To expand a collection in window view, right-click (on a Mac, control-click) the collection and select Restore.
To learn about building or re-sorting a playlist while you're watching a video, see To build or re-sort a playlist while watching a video.