Microsoft Excel is an example of a program that is not easy to launch directly: the path to Excel may be different, depending on Office version and platform (32-bit or 64-bit).
PowerShell has a very clever cmdlet to run programs: Get-Process. Traditionally, you'd use it like this to run Excel (or any other executable):
On your system, the path to Excel may be very different, though. Which is why Start-Process happily accepts wildcards. Just replace any "specific" part of your path with a wildcard, and you are all set.
This line will launch any Excel version, regardless of a platform: