In a multiplayer environment, there is no need to install it on the Server side

• Ctrl+RMB on a slot allows you to use the item from within the Gui (you can also operate levers or open chests)
• +Shift to use as if you were sneaking
• +Alt to place used items in your hand (for backpack items and the like)
• Ctrl+RMB on non-slot areas performs the standard RMB action while the Gui is open (this means using the item in your main hand. Even if you have nothing equipped, you can interact with blocks)

You can configure several settings in config/useitemwithingui-client.toml Show operation hints on the Gui

showHint = true

Press Ctrl+RMB outside the Gui to use the item in your hand

pressOutsideToUse = true