Welcome back to the productive non-lethal side of the world.
I wish you all the best in your recovery from military service and hope that unlike your handle, you are free of both insomnia and PTSD.
As CodeSmile points out, there is a way to use VSCode, but the official way is Visual Studio.
Remember you technically don’t need either one because Unity does 100% of the compilation when it builds. You technically could edit 100% of your code with Notepad if you wanted.
Here’s the skinny on Visual Studio, some of which may apply to VSCode:
This may help you with intellisense and possibly other Visual Studio integration problems:
Sometimes the fix is as simple as doing Assets → Open C# Project from Unity. Other times it requires more.
Other times it requires you also nuke the userprefs and .vsconfig and other crufty low-value high-hassle files that Visual Studio tends to slowly damage over time, then try the above trick.
Barring all that, move on to other ideas:
https://discussions.unity.com/t/778503
Also, try update the package inside of Unity: Window → Package Manager → Search for Visual Studio Editor → Press the Update button
Update: The VSC extension has been deprecated.
https://discussions.unity.com/t/886480
There is a community fork available that is receiving updates.
https://github.com/Chizaruu/com.tsk.ide.vscode
Also, this: https://discussions.unity.com/t/805330/7