VMware Cloud on AWS is an on-demand service that enables you to run applications across vSphere-based cloud environments with access to a broad range of AWS services. Powered by VMware Cloud Foundation, this service integrates vSphere, vSAN and NSX along with VMware vCenter management, and is optimized to run on dedicated, elastic, bare-metal AWS infrastructure (Source: Vmware official website)
So what is there from VMware and what AWS is providing ?
1) AWS is providing a dedicated infrastructure for this service to run all the VMware SDDC Stack (vSphere, NSX,
2) All the VMC management components are managed and maintained by VMware.
3) VMware is responsible for billing of all the VMC components.
4) Regular updates for SDDC components (NSX, vCenter etc.) is managed by VMware.
5) VMware cloud portal is the single place to deploy or manage the services (https://vmc.vmware.com)
You can use this solution as a standalone vSphere environment on AWS hardware or you can connect you on-prem vCenter and SSO to VMC vCenter with HLM (Hybrid Linked Mode).
Also if you need to connect VMs in your SDDC with resources in an Amazon VPC that isn't connected to your account using a cross-VPC ENI, you can create a VPN connection between your compute gateway and that VPC.
Site recovery manager is now available with VMC on AWS to protect your on-prem VMs to cloud (DRaaS), which makes it easy to protect your VMs in AWS datacenter using VMC on AWS.
This is only a beginning VMware is continuously working to add more components , features to this solution. and there is a long way to go......
A good place to start with VMC on AWS is the faq page