Start with a simple foreach loop to iterate through the list of your clusters:
Install certificate: Install-NcSecurityCertificate -Vserver <SVM> -Type <type> -Certificate <cert>
Modify CIFS security settings: Set-NcCifsSecurity -VserverContext <vserver> -UseLdapsForAdLdap $true
Validate settings have been applied successfully: Get-NcSecurityCertificate and Get-NcCifsSecurity cmdlets, respectively.
You may already know this, but the "Get-Command" and "Get-Help" cmdlets are awesome! I have not come across your specific use case before but just searched using Get-Command like this: "Get-Command -Module DataONTAP *security*" and the CIFS security cmdlets were returned as results (among others). From there, I just used "Get-Help" for cmdlets that looked like what I wanted, and read the documentation to figure out the syntax.
If you write some code and are having struggles, post a thread and we'll help debug. Hope it helps - happy automating!