This floater controls some of the ways that WWMT works in general. Things you set here will be set for the current Windows User's account for all following sessions running WWMT.
Attachments are points on your model where you can attach extra models and particle systems (guns, sprites, etc). This page details both Attachments and Particle Systems since the Particle System controls are also in the attachment rollout.
This rollout displays all of the LOD (Level of Detail) models in your model. Inside this rollout you can select the helpers that control LOD switch distances, vertex count percentages and add/append models to your LOD models.