A stopped instance does not incur charges, but all the resources that are attached to the instance will still be charged.
For example, you are charged for persistent disks and external IP addresses according to the price sheet, even if an instance is stopped.
To stop being charged for the attached resources, you can reconfigure a stopped instance to not use those resources, and then delete the resources.
Here is some documentation that could help you:
Stop and start a VM: https://cloud.google.com/compute/docs/instances/stop-start-instance
gcloud alpha compute instances suspend: https://cloud.google.com/sdk/gcloud/reference/alpha/compute/instances/suspend
Suspending and resuming an instance: https://cloud.google.com/compute/docs/instances/suspend-resume-instance
Save money by stopping and starting Compute Engine instances on schedule: https://cloud.google.com/blog/products/storage-data-transfer/save-money-by-stopping-and-starting-compute-engine-instances-on-schedule