If you don’t know what BGP is you probably don’t need to know about it . It’s only really needed for configuring large networks.
Many enterprises use it for their connectivity. If you are multihomed it's basically essential.
Even if you are not multihomed BGP is the most robust way to handle failover between two uplinks to the same ISP. If you are not using full routes and just taking default from each ISP the requirements/load on your router(s) are almost nothing.
Another popular use case is inside private networks, especially over GRE tunnel meshes where the filtering features of BGP allow better/easier control over topology than OSPF.
I've even seen individual servers use BGP for anycasting (usually DNS servers) or http load balancing (with DSR and L4 hashing on the upstream router).
Like the Internet... way to understate it.