Bitcoin core tutorial & code walk through (Part 1)

Bitcoin core is the reference implementation of Bitcoin code.

1) Download Bitcoin core from github
https://github.com/bitcoin/bitcoin

2) Build it
/autogen.sh
./configure --enable_debug
make
make install

3) Setup the bitconf.conf. In the minimum, setup the rcpuser and rpcpassword field
bitconf.conf configuration file path:
OS                Default bitcoin datadir      Typical path to configuration file
Windows     %APPDATA%\Bitcoin\     C:\Users\username\AppData\Roaming\Bitcoin\bitcoin.conf
Linux           $HOME/.bitcoin/               /home/username/.bitcoin/bitcoin.conf
Mac OSX    $HOME/Library/Application Support/Bitcoin/             /Users/username/Library/Application Support/Bitcoin/bitcoin.conf

4) Useful commands
bitcoind -daemon  ; bitcoin-cli stop      - start and stop bitcoin daemon
bitcoind -printtoconsole                        - print debug message to console
bitcoind -daemon -proxy=192.168.1.1:80   - run bitcoind w/o downloading new blocks
bitcoind -testnet    bitcoin-cli -testnet      - run in test network
bitcoind -regtest    bitcoin-cli -regtest     - run in regression test network
bitcoind -debug=rpc                              - set the debug level

bitcoin-cli getblockhash <number>
bitcoin-cli getblock <hash>
bitcoin-cli getblockcount
bitcoin-cli -regtest getblockchaininfo
bitcoin-cli -regtest generate 500      - mine 500 blocks
bitcoin-cli -regtest getbalance          - check rewards

5) Source code walk through is based on v0.14.99.0 (bitcoind -version)
bitcoind.cpp  
main() calls AppInit()
AppInit() calls AppInitParameterInteraction()
then calls AppInitMain(threadGroup, scheduler) - main init function
init.cpp
AppInitParameterInteraction() - setup debug level, register RPC commands
AppInitMain()
            lock directory
            start lightweight task scheduler thread
            AppInitServers() -  start App servers, such as HTTP, RPC servers
            RegisterNodeSignals(GetNodeSignals())
            create zero message queue
            cache size calculations
            LoadBlockIndex(chainparams)
            check genesis block
            InitBlockIndex(chainparams)
            InitLoadWallet()
            GetConsensus()
           CConnman::Start(scheduler, connOptions)
           wallet->postInitProcess(scheduler)
net.cpp
CConnman::Start(...)     - start threads to accept connections, process messages
call InitBinds(std::vector<CService>&, std::vector<CService>&) - bind to address and port number
InitBinds() call GetListenPort()
validation.cpp
LoadBlockIndex(chainparams)        - load block index from db
GetBlockSubsidy(nHeight, consensusParams)       - get mining block rewards
merkleblock.cpp
CMerkleBlock constructor initialises CPartialMerkleTree
CPartialMerkleTree constructor calls TraverseAndBuild()
net_processing.cpp
ProcessMessages->ProcessMessage->ProcessGetData->CMerkleBlock
net.h
RegisterNodeSignals->CNodeSignals.ProcessMessages
init.cpp 
RegisterNodeSignals
rpc/server.cpp
StartRPC()  - called by AppInitServers
httpserver.cpp
StartHTTPServer()  - clled by AppInitServers
util.cpp
LogPrintStr
util.h
LogPrint          - debug log macro
LogPrintf         - debug log macro
LogAcceptCategory   - check the BCLog category and decide to print log or not
httprpc.cpp
HTTPReq_JSONRPC(HTTPRequest* req, const std::string &)     - parse the rpc request that is sent from bitcoin-cli