Hi @Marouf Ali ,
basically you already mentioned the main difference between Azure Express Route and peering of Azure Virtual Networks.
The peering of Azure Networks (vNets) is for connecting Azure vNets.
The Azure Express Route offers to connect from on-premises/private networks to Azure Networks.
Beside the technical differences there is a difference in pricing as well ;-)
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Andreas Baumgarten