Did you try to search for it? There are literally thousands of examples all over the internet and probrably even hundreds here in this forum. Take a look at the cmdlet Add-ADPrincipalGroupMembership and read the complete help including the examples, please.
I have searched. Everything I find is for adding the systems in an OU to one group not multiple groups. I am willing to accept that I can’t find the answer at this point and this is the reason I posted the question here. Either way I will keep looking. Thank you for your reply.