Add Users to SharePoint Group using PowerShell

#Get the site name to the variable
$web = Get-SPWeb SitURLHere
#Get the group name to the variable
$groupName = $web.SiteGroups["Group Name Here"]
#Assign user to variable
$user = $web.Site.RootWeb.EnsureUser(“User ID Here”)
#Add user to group 
$groupName.AddUser($user)
Write-Host -ForegroundColor green "User Added Successfully";