The Level of Detail Generator on the Level of Detail Tools Rollout lets you generate LOD models from the root mesh. The tool will make lower-res versions of your model so that less polygons are rendered in-game when players move farther away.
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.