What is self leveling sand step 2? In the description it says use with it

Thanks for your question. Leveling Sand is a sand used over paver base when setting pavers to ensure you set pavers or retaining wall blocks on a smooth and level surface. It is typically applied over paver base in a 1" thickness. It can be used for: Interlocking pavers, retaining walls, stepping stones, bricks, and natural stone