How do you put roblox starter packs into the game

You need to be in Roblox Studio to do this. From there, click View and make sure Properties, Explorer, and Toolbox are open. Click a tool from the Toolbox; if you get a notification asking if you want to place the tool in StarterPack, click yes. If no dialog comes up, find the item in Explorer under Workspace and drag it to the service named StarterPack.

If you are a developer or want to script your own tools, you can insert the basic parts from Insert > Object and move them to the StarterPack.