The quickest way how to deploy wordpress including an MySQL database for free is via a simple template
https://azure.microsoft.com/de-de/resources/templates/wordpress-app-service-mysql-inapp/
az group create --name <resource-group-name> --location <resource-group-location> #use this command when you need to create a new resource group for your deployment
az group deployment create --resource-group <my-resource-group> --template-uri https://raw.githubusercontent.com/Azure/azure-quickstart-templates/master/wordpress-app-service-mysql-inapp/azuredeploy.json