Azure load balancer works on layer 4 and distributes the traffic across the VMS. The load balancer is of 2 types, Internal load balancer which used to the internal application and external load balancer which used for external application. Let say if you have a web application running on a set of VMs and you want to load balance then internally or externally then you can utilize the Azure load balancer. You can configure the health prob and another rule for your web application. Even if you want to apply the NAT rules you can set up the same.