What is the purpose of bgp ?

The main purpose of BGP is to exchange routing updates like other routing protocols, but BGP typically does not exchange individual network routes (but it technically can), it exchanges summaries of network routes. This is because the typical use of BGP is over very large networks including the Internet.

Port Number of BGP?

BGP uses TCP port 179.

BGP is IGP or EGP?

BGP is an EGP(exterior gateway protocol). Exterior Gateway Protocols handle routing outside an Autonomous System and get you from your network, through your Internet provider's network and onto any other network.

But Interior Gateway Protocols (IGPs) handle routing within an Autonomous System.

Can I run two BGP process on single router?

No, You cannot run two BGP process on a Single Router.

Can I use BGP instead of any IGP?

No, because bgp works between autonomous systems but igp works inside of autonomous systems.