This mod contains a few features, first of all - Inventory HUD, it shows your inventory while you are playing, you can switch between mods (mini/normal and horizontal/vertical), also you can change background transparency and toggle animation on/off

Next feature is PotionHUD, it shows your potion effects with timer or duration bar if you are using mini mode, you can change gap between effects and background transparency in config, and you can enable horizontal mode as well

And last but not least feature is ArmorHUD, it shows durability of your armor and equipment, also shows how many free slots do you have in your inventory and how many arrows do you have. This HUD is fully customizable, you can change scale, type of damage indicator or turn on/off each part of your equipment

You can change a lot of options in config ("Mod" button in Main Menu, then "Config"), also you can change the position for each HUD by simply dragging and dropping them. To open ingame config screen you can use keybind ("O" by default)