I have 3 link of internet.
I want to make 2 Links working on same time ( Loadbalancing) and 1 will connect as stand by. So anyone link down from loadbalancing Links, Stand by will start working automatically to balance load.
Why don’t you want to simply load balance all 3?
As for the load balancing, feel free to look through the videos from US2012 MUM. Link for bandwidth-based load balancing in my sig.
As for the failover, feel free to take a look at this script on the wiki: http://wiki.mikrotik.com/wiki/Failover_Scripting
It monitors a certain IP using 2 gateways, and can increase the distance of routes when that IP becomes unpingable. You can configure it all, so if both links cant ping that IP, increase distance of their routes by a certain value, making sure that the 3rd backup connection is used.