Save the powershell's output in a CSV file

Use Export-Csv cmdlet:

Get-CimInstance Win32_OperatingSystem | Select-Object Caption, CSDVersion, ServicePackMajorVersion, BuildNumber | Export-Csv -NoTypeInformation -Path .\OS_Info.csv

Result (OS_Info.csv):

"Caption","CSDVersion","ServicePackMajorVersion","BuildNumber"
"Microsoft Windows Server 2012 R2 Datacenter",,"0","9600"

Thank you it worked, the file is generated in the folder System32

As Rohin Sidharth mentioned, .\ prefix for the path will create file in the current dir ($PWD in PowerShell). You probably run PowerShell as administrator: in this case the default directory is %WinDir%\System32. Just use full path or GetFolderPath .Net method to get common folder path, like desktop:

... | Export-Csv -NoTypeInformation -Path 'C:\OS_Info.csv'
... | Export-Csv -NoTypeInformation -Path (Join-Path -Path [System.Environment]::GetFolderPath('Desktop') -ChildPath 'OS_Info.csv')

Can you also show me how to export many results in the same file ? for example i have a script in which i can know all the update that are installed :

Get-Hotfix | Select HotfixID,Description,InstalledOn | Sort InstalledOnfunction

and i want the results saves in the same CSV file

You can do this by using Select-Object's calculated properties:

# Get OS info
$OsInfo = Get-CimInstance -ClassName Win32_OperatingSystem

Get-Hotfix | # Get HotFixes
Sort-Object -Property InstalledOnfunction | # Sort them
Select-Object -Property @( # Select required fields

    # Add Caption property from $OsInfo variable
    @{
        Name = 'Caption'
        Expression = {$OsInfo.Caption}
    }

    # Add CSDVersion property from $OsInfo variable
    @{
        Name = 'CSDVersion'
        Expression = {$OsInfo.CSDVersion}
    }

    # Add ServicePackMajorVersion property from $OsInfo variable
    @{
        Name = 'ServicePackMajorVersion'
        Expression = {$OsInfo.ServicePackMajorVersion}
    }

    # Add BuildNumber property from $OsInfo variable
    @{
        Name = 'BuildNumber'
        Expression = {$OsInfo.BuildNumber}
    }

    # Add other properties from original HotFix object
    'HotfixID'
    'Description'
    'InstalledOn'

) | Export-Csv -NoTypeInformation -Path 'C:\OS_Info.csv'

You can also try to join objects using custom function.

Quick tip: Make sure you don't pipe to Format List (FL) then pipe to export-csv or you'll open the CSV file and your data will look like this.

ClassId2e4f51ef21dd47e99d3c952918aff9cd pageHeaderEntry pageFooterEntry 
autosizeInfo    shapeInfo   groupingEntry
033ecb2bc07a4d43b5ef94ed5a35d280                
Microsoft.PowerShell.Commands.Internal.Format.ListViewHeaderInfo    
9e210fe47d09416682b841769c78b8a3                    
27c87ef9bbda4f709f6b4002fa4af63c                    
4ec4f0187cb04f4cb6973460dfe252df                    
cf522b78d86c486691226b40aa69e95c