Open in the Windows PowerShell ISE in your Local PC. 

Then, How to Connect your Azure Portal account. Command: 

Connect-AzureRmAccount 

After, Create a new resourcegroup or used already created.  Command: 

New-AzureRmResourceGroup -Name webresGroup -Location 'East US'

Then, Create an WebApp Service plan in Free/Standard tier.

New-AzureRmAppServicePlan -ResourceGroupName webresGroup -Name webapp -Location 'East US' -Tier Standard

After,finally you are Create a New web app in your Azure Portal.

New-AzureRmWebApp -ResourceGroupName webresGroup -Name powershellwebapp -Location 'East US' -AppServicePlan webapp

Then,  Opening the your Azure Portal before create new webapp. See App Services

After, Created New WebApp . Lets see your App Service, New WebApp here.