Area1
This is the click and move area. Clicking on any of the buttons here will start shaping the f-curves of the selected keyframes. After you click for the first time on any of the icons an "Amount" slider will appear. Moving the mouse to the right will increase the amount to up to 1; moving it back to the left will decrease the amount. As the name suggests, that slider is a real time indicator of how much the selected curves are being affected.

Click again to apply the changes. Drag the mouse all the way for the amount to get to 0 and then click if you don't want any changes.

Note #1: every function has a requirement on how many keyframes need to be selected for it to work. Each button's tooltip tells you how many you need to have selected.  If the keyframe includes several f-curve keyframes, the count is per f-curve. Say, Exaggerate requires you to have exactly two keyframes selected. You can use it on as many f-curves at once as you want as long as each of the affected f-curves has two keyframes selected on it. The example below will work for Exaggerate:

Note #2: As of version 1.02, every function has a smart keyframe deselect feature when working with armatures. What it does is simple. If you have a bone selected, it will only affect the keyframes associated with this particular bone. If no bone is selected, it will affect all the selected keyframes. This function allows you to cycle through bones, animate them and not worry about having to spam deselect keyframes every time you select a new bone. Without this function, unless you spam Alt+A, you can accidentally affect keyframes you don't want to be affected.

Preview in the Graph Editor: as the name suggests, enabling this check will zoom the view to the affected keyframes. The preview will happen on one of the Graph Editors in your workplace, if there's one open.

Area 2
This area contains a set of tools that aren't gradual. To use them simply click on them without dragging.

Note: Both Auto-bounce and Extrapolate Keyframe depend on your playhead position. Both will either move or create a keyframe at it. For auto-bounce, the further away your playhead, the heavier the recoil from the bounce.

Area 3
This group of tools let you manage the quick noise effect. Thanks to them you can access the noise modifier straight from both the Timeline and Dope Sheet editors. Adding noise will turn the keyframes green.

• Add Noise: Select two or more keyframes and the addon will add noise between them. Keyframes with noise will be marked green. Can add multiple instances of noise per f-curve.
• Remove Noise: Select the green keyframes you want to remove noise from.
• Edit Noise: Select any keyframe from the f-curve you want to edit the noise modifiers of. If it has more than one noise modifier, you will be able to choose which one to edit.

Area 4
This group includes two toggleable handlers and a settings area. Do note that the handlers might make the UI a bit laggier in complex projects and on slower systems.

• Armature Mode: When toggled ON, Blender will deselect all keyframes every time you select a different bone; This way you'll avoid having keyframes from unused channels staying quietly selected in the background.
• C4D/Maya Mode: Every time a new keyframe is created, Blender will select it by replacing the previous selection rather than by adding to it. This mimics the way it works in Cinema 4D and Maya.
• Display In the Graph Editor: turning this setting on will create a copy of the entire Simple F-Curves panel in the Graph Editor.
• Respect Object Selection: When ON: before performing any operation, the addon will deselect any keyframes from objects that aren't selected. When OFF, the addon operations will affect ALL selected keyframes no matter whether their respective objects are currently selected. Default: ON