Identifying transactions related to gateways

[Shubham_Anand]

I was looking into the ripple protocol. I got really confused regarding the roles of the gateways in the network. 

My questions specifically are--

1. Suppose a person A has to send x amount of some currency he has into some other currency to person B. What are the exact steps that should be followed by A and what does the protocol exactly do the above transaction. What role does the gateways play in the above setting?

2. As gateways are the entities which bring in non XRP currencies into the XRP network. How exactly does it do that? 

3. How can we distinguish between the transactions in a ledger version which are related to actions done in part-2 above ? I mean transactions that come in the network due to a gateway.

Please provide any other information related to gateways which might be useful for understanding the above scenarios.

Thankyou.