How to add another WAN link

I have two static IP running already now I have another new connection two with PPPOE username and password. So, how to i establish new WAN without disturbing my old network.?

Maybe these are a good place to start:

Failover WAN
https://wiki.mikrotik.com/wiki/Advanced_Routing_Failover_without_Scripting

A load balancing WAN:
https://wiki.mikrotik.com/wiki/Manual:PCC

Thank You. Can You suggest me easiest way to study, other’s network.?