One of the major changes that you will face when you move from on-premises cloud to the public cloud is the switch from capital expenditure (buying hardware) to operating expenditure (paying for service as you use it). This switch also requires more careful management of your costs. The benefit of the cloud is that you can fundamentally and positively affect the cost of a service you use by merely shutting down or resizing it when it's not needed.
https://docs.microsoft.com/en-us/azure/architecture/cloud-adoption/appendix/azure-scaffold

An Azure virtual machine is an example of Infrastructure as a Service (IaaS).
Azure web app, Azure logic app and Azure SQL database are all examples of Platform as a Service (Paas).
https://azure.microsoft.com/en-gb/overview/what-is-iaas/
https://azure.microsoft.com/en-gb/overview/what-is-paas/