This form is displayed from the Block - Blocks to Layers tool.
The form will give different result depending on the current block of the layer.
If the current block is the drawing layer, then the Available blocks list will contain all the blocks at the top level. Highlight the blocks you wish to create drawing layers from and move them across to the right hand column. Press OK and the blocks will be converted to drawing layers and the block insertions will become layer insertions.
If the current block is a sub-block, then the Available blocks list will contain all sub-blocks within the current block. Highlight the blocks you wish to create drawing layers from and move them across to the right hand column. Press OK and drawing layers will be created from copies of these blocks. The new layer names will be the same as the original block name and the blocks in the current layer will be renamed to include _1, so that they have unique names.
Blocks to Layers