When you use double-quoted strings, you can expand variables inside of them like this:
PS C:\> "Windir: $env:windir" Windir: C:\Windows
However, there is no obvious way to mark the beginning and end of variables, so this will fail:
PS C:\> "$env:windir: this is my Windows folder" this is my Windows folder
The solution is to use braces to identify the start end end of variables inside strings:
PS C:\> "${env:windir}: this is my Windows folder" C:\Windows: this is my Windows folder