First, select the build you want to export by selecting all of it. You can either do this manually or select it by holding down left click and dragging over your build like this:
Then, click the export button in the dock of the tool.
A panel will open with your creation’s code. You will need this code to export your build. YOU MUST KEEP THIS PANEL OPEN IN ORDER FOR THIS TO WORK!
Then, open Roblox studio. Now you can either create a new game or open up a pre-existing game.
From here, install this plugin.
F3X Importer
Now, go back to Roblox studio and go to the toolbox. (in the home tab above)
Choose the plugins category.
Now find the importer plugin, click it, and press install.
Now find the ‘plugins’ tab at the top of the screen, enable the import plugin, and enter your code.