That’s all it is, just vector math: add the position you want in.
If I am at myPosition and I want to randomly pick around me in a radius meter circle, the expression would be:
Vector3 randomSpotNearby = myPosition + Random.insideUnitCircle * radius;
BTW, you misspelled Random.InsideUnitCircle… the first i must be lowercase.
The editor SHOULD be fixing that for you. If not, read this:
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 VSCode package inside of Unity: Window → Package Manager → Search for Visual Studio Code Editor → Press the Update button
Also, this: https://discussions.unity.com/t/805330/7