1. Insert the Host GUI
This page will guide you through getting the model and inserting it in the right place in your game.
1.1. Add the model to your Toolbox
Press the Creator Store button below to get taken to Roblox's creator store. When you're there, press the Get Model button. This will put the Host GUI into your Toolbox.
1.2. Insert the model into your game
Open your game in Roblox Studio. Open the Toolbox window and go to the Inventory tab. Drag the Host GUI into your game.
Open the Explorer window. Open Workspace and drag the HostGui folder into ServerScriptService.
The Explorer window contains everything in your game. There are multiple 'folders' you can put stuff into. Workspace usually contains everything that's visible or interactible. ServerScriptService is a special folder for scripts. Technically there aren't any requirements for the Host GUI to be there, but it's a nice way to keep your game organised.
1.3. Test if everything works correctly
By default, the control button of the Host GUI is not whitelisted, so you should be able to access it without changing anything. Start the game. You should see a 'chat' icon on the right side of your topbar. Select it and send anything in chat. If everything works correctly, you should see the Gui appear.
Topbar+ warning
If you're using Topbar+ in your game for topbar icons, the version of it in your game might interfere with the version bundled with the Host GUI.
This is because models inserted from the Toolbox are sandboxed by default, but Topbar+ is on a list of manually excluded assets and is not sandboxed. This mix of sandboxing means that when the Host GUI tries using the Topbar+ you have in your game already, it fails to run it, causing the entire system to fail.
To fix that, you should disable sandboxing on every script in the Host GUI model. You can either do that manually or by selecting the Host GUI folder and running the code below in the Command Bar in Studio (you can enable it in the Script tab):
for _, instance in game.Selection:Get() do for _, script in instance:QueryDescendants("LuaSourceContainer") do script.Sandboxed = false end end