difference between EAP-TLS and EAP-TTLS and how to configure them on a NPS?

Hi,

I think the title says all already. I'm still trying to understand something in the chaos of authentication protocols. I know that both EAP-TLS and EAP-TTLS need certificates on both the authentication server AND the clients, but what's the difference between them?

And is there a guide somewhere to know how to set EAP-TLS or EAP-TTLS on a Microsoft NPS server?

Thank you in advance