if the MCM menu for "Spell Hotbar" does not show up for you try
setStage SKI_ConfigManagerInstance 1 and wait a bit. This will tell MCM to reinit the menus.

The 12 keybinds are obviously the bindings for your 12 slots. When you bind 1-8 while using default skyrim keybinds there will be a warning that this is already bound to Hotkey#. This is not a problem unless you also use the hotkey in your favorites menu, then 2 actions will be triggered at the same time. If you want to unbind or rebind the default 1-8 keys you can to it via controlmap.txt.

The Previous Bar and Next Bar buttons are only used while inside the magic menu while binding your spells. Depending on which weapon you are holding the bar wills switch, when you open the menu the current bar will be active, but then you can cycle through your bars by using this hotkeys. If you disable all bars except the main one, you do not need to bind this buttons.
Suggestions for binds that do not clash easily: PageUp/PageDown, Numpad 4&6

• Enable CTRL/SHIFT/ALT Bars: Every bar will get an additional set of 12 bindings when a modifier key is held down. (To use shift in the bind menu you need to rebind SkyUIs switch between Inventory and magic menu in it's MCM)

• Show HUD Bar: change when the hotbar is shown, this can be always, never or depending on your combat or draw weapon state. Vampire Lord and Werewolf have limited options are drawn weapon is not applicable in their state. In unmodded Skyrim Werewolf is useless and does not have bindable actions, therefore it defaults to Never.

• Use Default bar when Sheated: The mod switches your bar depending on your equipped weapon(s), also if the weapon is sheated, this setting will change the behavior to switch to the default bar when you have not drawn your weapon.

• Disable Menu Rendering: Hide the rendering in the menu, you can still blindly bind your spells.

• Slot Scale: Change the size of the slots, 1.0 is rather large, most users will probably happy with something in between 0.65 and 0.8
• Slot spacing: Amount of space between two slots in pixels
• Offset X: shift bar away from default position in pixels in X axis
• Offset Y: shift bar away from default position in pixels in Y axis

The default position is calculated relatively to your resolution, depending on your res you will need different offset values to shift your bar.

• Enabled: enable this specific Bar, if a Bar is disabled it's parent bar is used instead, the default bar cannot be disabled.
• Inherit Mode: change how this bar inherits from parent. If you do not use modifiers (ctrl,shift,alt) only disabling inheritence is relevant. Otherwise you can change if the non-modifier bar is inherited or the parent's bar with the same-modifier. e.G: "CTRL-Ranged" inherit from "Ranged" or "CTRL-Default".

This allows you to load & save the MCM config or your slotted skills to/from .json file.

There are already 3 config presets bundled with the mod:

• Default: the default state of the MCM after installing the mod, (no keybinds)
• Simple: Some bars disabled, bar is smaller, 1-12 bound to hotkeys, Numpad 4&6 for the Menu binds. Quickstart option
• Minimal: Just the default bar, bar is smaller, 1-12 bound to hotkeys

I do recommend to start with most bars disabled when starting a new game and add new bars/modifiers as you need them when you acquire more skills.

Saving your Bars is mostly interesting for mod updates (clean saves...) or transfering your loadout between saves.

• Reload Resources: Only needed when you create your own spell configs, this will reload all images without needing to restart the game. (Currently Fonts are not reloadable)
• Reload Spell Data: Only needed when you create your own spell configs, this will reload all spell settings without needing to restart.
• Clear all Bars: Every slot on every bar will be empty after this.
• Drag Bar: Show a draggable window to scale/reposition the bar. Mouse input will be captured during this and not forwarded to the game. You can leave the mode by pressing ESC or the X on the frame. You can leave the menu with tab during this mode to see the position in your ingame UI.