How do I combine two separate networks from two different ISP?

RouterOS Beginner Basics
1

I want to create a common path between two isps so that data from ISP 1’s LAN can flow to and from ISP 2’s LAN.

2

You mean to create a ptp link between 2 routers with differents isp? You can use IPsec for security but cant use OSPF because IPSec dont allow multicast, or EoIP Tunnels.