The Kubernetes cluster is composed of multiple Nodes - each node is a Compute Engine Virtual Machine. When you deploy a container image into Kubernetes, a container instance is ultimately scheduled and ran on one of the Nodes.
In Kubernetes Engine, theses nodes are managed by a Node Pool, which is a set of homogenous Compute Engine Virtual Machines (i.e., they have exactly the same configuration, such as machine type, disk, operation system, etc).
You can add different machine types to your Kubernetes Engine cluster, by creating a new Node Pool with the configuration you want.
You can see a list of Virtual Machines using gcloud:
gcloud compute instances list
You can also use kubectl to list the nodes that belong to the current cluster:
kubectl get nodes
You can also SSH into the node directly if needed, by specifying the name of the node: