Sorry but it is not clear to me if you are announcing a tutorial that you are preparing right now or you are requesting a tutorial. Whatever, issuing a cert for a free dynamic domain follows the same procedure as for a “normal” domain.
The only thing is that you will need to issue the cert using http or tls challenges, you can’t use dns challenge to validate the free dynamic domain, maybe some free dynamic domain allow to add the TXT records needed for the DNS challenge to their DNS servers but I doubt it.
The other thing you should take care is that the parent domain of the DDNS server that you will use needs to be included in the Public Suffix List (here is the list) or it could be near impossible to issue a cert for the domain because you will hit the rate limits.
Thank you for the interest shown. It is perfectly clear that what I am exposing is a setup base, from wich I will create an ssl certificate using let’s encrypt.