$siteUrl = <url to your sitecollection>
$username = <username>
$password = <password>
add-type -Path ".Microsoft.SharePoint.Client.dll"
add-type -Path ".Microsoft.SharePoint.Client.Runtime.dll"
$clientContext = New-Object Microsoft.SharePoint.Client.ClientContext($siteUrl)
$securePassword = ConvertTo-SecureString $password -AsPlainText -Force
$clientContext.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($username, $securePassword)
$site = $clientContext.Site;
$clientContext.Load($site)
$clientContext.executeQuery()