Hi Will,
The Adjustments Inspector shows you all of the currently applied adjustments. There may be other Adjustment Bricks showing -- the ones with a checkmark in the box at the upper-left are applied.
You can toggle any adjustment on/off by checking/unchecking this checkbox.
LR users are usually befuddled that there is no "history". What you see is the current state of the Image. All the adjustments you've made are contained in the Adjustment Bricks (whether they are being applied or not). The order in which the adjustments are applied is fixed. (It is because the order is fixed that a history of when _you_ applied each adjustment is meaningless.)
If you have used a Brush to create an adjustment mask, you will have to bring up the Brush HUD to show the mask. Click the Action Menu (a/k/a "the gear") icon and select from any of the selections that show you the adjustment mask.
In addition to toggling the application of an adjustment on/off, you can reset the adjustment to its default state, and you can remove the adjustment from the Image. Click the little curved arrow on the upper-right of the Adjustment Brick to return the settings to their defaults. Select the Brick, and press and release the "{delete}" key to remove the adjustment from the Image.
HTH. Recommend you read the first seven chapters of the User Manual -- they provide a thorough introduction to Aperture's UI.
--Kirby.
