Whenever you deploy a resource into Azure you have to deploy them into a resource group. Over time you may discover that you need to move the resource to another resource group or even subscription. Example of a move could be, a particular VM now belongs to App B so you need to move it to the resource group where all the App B resources are.
Now not all resources can be moved to another resource group or subscription so here is this handy article from Microsoft where you can check if the resource can be moved between resource group or subscription.
One key point to remember is that moving the resource does not actual move or change the location of the resource. You are only changing the location of where you are managing the resource from. So if you have deployed a VM in North Europe in resource folder A and decided to move this resource to resource folder B. The VM will continue to run from North Europe but the management of the VM would be from resource folder B.
Below is any article on some key checks before you move the resources and various examples on how to move the resource using the Azure portal, powershell, Azure CLI or REST API.