In GCP, a VM instance is quite similar to AWS EC2. You can choose from a variety of machine (instance) types that have different hardware configurations; you can also choose a Linux-or Windows-based OS or your customized OS.
As mentioned when talking about firewall rules, you can specify any number of network tags. A tag doesn't necessarily need to be created beforehand. This means you can launch VM instances with network tags first, even though a firewall rule isn't created. It's still valid, but no firewall rule is applied in this case. Then you can create a firewall rule with a network tag. Eventually a firewall rule will be applied to the VM instances afterward. This is why VM instances and firewall rules are loosely coupled, ...
