Recent Sitecore 9.1 Initial Release had launched with SIF 2.0. As per documentation you need to execute following command. Assuming here you are doing first time on your machine.

```
Register-PSRepository -Name SitecoreGallery -SourceLocation https://sitecore.myget.org/F/sc-powershell/api/v3

```

But this gives me error on my local machine & tried also in my remote fresh Azure Windows Server 2016 machine. Following is error

```
PackageManagement\Register-PackageSource : Module Repository 'SitecoreGallery' exists.
At C:\Program Files\WindowsPowerShell\Modules\PowerShellGet\1.0.0.1\PSModule.psm1:4173 char:17
+ ...     $null = PackageManagement\Register-PackageSource @PSBoundParamete ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ResourceExists: (Microsoft.Power...erPackageSource:RegisterPackageSource) [Register-PackageSource], Exception
    + FullyQualifiedErrorId : PackageSourceExists,Microsoft.PowerShell.PackageManagement.Cmdlets.RegisterPackageSource

```