If IntelliSense isn't working for you in VS Code there are a few simple steps you might want to try.
First, have you tried turning it off and on again?! Give your computer a quick restart and see if that helps. Sometimes this is all you need after some new software has been installed.
If that didnt work, make sure that youve set VS Code as your preferred external editor in your Preferences.
In Unity, go to: Edit > Preferences > External Tools. Then, set your External Script Editor to Visual Studio Code.

Note: Direct support for VS Code in Unity was dropped in 2022. If VS Code is not appearing in the list, you will need to browser to the location where you installed the it.
To make setting up your External Script Editor a little easier, you may want to try installing the Visual Studio Code Package from the Package Manager. This package has now been depreciated by Unity but it should still appear under the Unity: Registry tab.

If its still not working the next step is to double check that you have the correct .NET framework installed on your machine.
Start with the latest .NET Core SDK and .NET SDK packages, which you can download from https://dotnet.microsoft.com/download
You will also need to install the .NET 4.7.x (Developer Pack), which you can download from https://dotnet.microsoft.com/en-us/download/dotnet-framework/net47
Once these are installed, give your computer another quick restart.
Note: you may need to head back into your Preferences and check that VS Code is still set as your External Script Editor.
Next on the list is to open up VSCode and check that the correct solution workspace is selected.
Press Ctrl+Shift+P to open the command palette
Then type Omnisharp: Select Project
Finally, chose the solution workspace (.sln) for the project youre currently working on
One final option is to tweak some of the settings in the C# Extension you added to VSCode.
In the extensions panel; select the C# extension, click on the cog icon, and then select Extension Settings. This will open up an new window and you want to scroll down the list until you find Omnisharp: Auto Start and check this option.

If you are getting an error in VS Code that says Project Not Loaded in the bottom right corner, you may need to try the following:
Uninstall the C# extension (along with any dependencies)
Reload VS Code
Reinstall the C# extension
Now, if you've done that and you're still having trouble, let our awesome teaching assistants know and they will do their best to get you up and running!
If youre exhausted from tinkering with VS Code then remember that the script editor you use is largely a personal choice. If you really cant get VS Code working, try something like Visual Studio Community.
This will look different to the code editor used throughout the rest of the course and many of the hotkeys will be different. However, it still allows you to write your code and should allow you to follow along with the course just fine!