Composites are the output of the generative process. After you Generate New Composites, you can review the composed artwork and metadata, and the resulting Rarity Chart for the Drop.
While reviewing, you can click on a Composite for additional options:
Delete: you can delete individual Composites, but be aware, this will reduce your Drop's total supply. (If you plan to curate your output in this way, it might be advantageous to compensate by generating a larger supply, and then deleting until you reach your original target.)
Add Additional Metadata: you can more metadata on a one-by-one basis. (This might be useful if you want to designate a few NFTs as special in some way, for example.)
When satisfied with the Composite set, you can proceed to Export for Candy Machine. This is the only time that a cost will be incurred if using the hosted version of Treat Toolbox. You will be prompted to provide payment before continuing.