Whait is ip source gaurd why we use and when we use?

This feature helps prevent IP spoofing attacks when a host tries to spoof and use the IP address of another host. Any IP traffic coming into the interface with a source IP address other than that assigned (via DHCP or static configuration) will be filtered out on the untrusted Layer2 ports.

The IP Source Guard feature is enabled in combination with the DHCP snooping feature on untrusted Layer2 interfaces. It builds and maintains an IP source binding table that is learned by DHCP snooping or manually configured (static IP source bindings). An entry in the IP source binding table contains the IP address and the associated MAC and VLAN numbers. The IP Source Guard is supported on Layer2 ports only, including access and trunk ports.

So, Any mismatch in the binding table found the ip traffic will be blocked on that interface.