Pools are a unique type of container shape. The BPMN library in the Universal Model Editor contains both a Vertical and Horizontal pool shape.
By default, pool shapes have two lanes. Add lanes to the pool by clicking Add Lane near the bottom of the shape.
When moving a pool or using any of the shape commands, make sure the entire shape is selected by clicking on the outer border or the pool header.
Horizontal pools can only be re-sized horizontally; vertical pools can only be re-sized vertically. Lanes can be re-sized both vertically and horizontally.
When moving or deleting a lane, make sure the lane is selected by clicking anywhere inside it.