How do I find which Windows version I'm using?

I'm using PowerShell 2.0 and tried:

```
PS C:\> ver
The term 'ver' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify tha
t the path is correct and try again.
At line:1 char:4
+ ver <<<< 
    + CategoryInfo          : ObjectNotFound: (ver:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

```

How do I do this?