1. When a Client wants to send a Transaction ( Make payment ), how it knows the IP Address of the Network to which it has to send.
Is there any DNS Server managed?
The Bitcoin Network is a peer-to-peer (P2P) network. Any client or node in the network can be connected to any number of other nodes. They (in principle) all relay transactions, so just being connected to 1 is enough.
That said, if you are just starting your client for the very first time after downloading it, how do you find that first contact in the network? This "bootstrap problem" is common to all decentralized networks. The solution chosen for the main Bitcoin client is simply to hardcode the address of a server (technically an IRC server where other nodes join, backed up by a hardcoded list of "known good" nodes).
2. Where the transacation are stored before they are included in a Block.
The transactions are stored in the memory pools of the miners who are trying to complete the next block of the block chain. Most bitcoin clients will also resend the transaction if it isn't included for some reason.
3. How and where the nodes can check the Transactions which have to be included in the Block
No transaction HAS to be included in a block. The miners are free to chose which transactions they want to include and which they don't.
As for validating a transaction, that is simply a matter of verifying the cryptographic signatures. The information required to do that is contained in the block chain.
4. If a new Miner wants to add a node, How the Miner can get the IP address of the Network to which his/her Node can be added.
Any node can mine. Any node can submit a block solution to the network and it will become the next block in the block chain if valid (simplified a bit).
This question seems to overlap with question 1 and appears rooted in some misconceptions. For the detailed process about getting something to mine, you could look up getwork (
https://en.bitcoin.it/wiki/Getwork ), but that's probably more than you're asking for.