Hi @Krishna Aswin ,
Thanks for contacting Microsoft Q&A platform.
A user will need "VM Contributor role" or a custom role with privileges to power off\on, if they need to shutdown a VM via a portal or powershell or azure command line.
It is also possible to schedule a shutdown through "auto shutdown" feature, available in the left menu for vm under "Operations" > "Auto shutdown".
You can also operate VM's using below Powershell Query.
Connect-AzAccount #Authenticate to Azure
Set-AzContext -Subscription <subscription name> # set the correct subscription
Stop-AzVM -ResourceGroupName <Resource group> -Name <Virtual machnie name>
Hope this helps you.