There is a demo application where you can try BNB Sidechain. It already contains pre-deployed API gateways, block explorer, UI for the staking and faucet.
RPC Endpoint: https://rpc.dev-01.bas.ankr.com/
Block Explorer: https://explorer.dev-01.bas.ankr.com/
Staking UI: https://staking.dev-01.bas.ankr.com/
Network Name: BAS devnet
New RPC URL: https://rpc.dev-01.bas.ankr.com/
Chain ID: 14000
Current Symbol: BAS
If you want to see BNB Sidechain source code, check the BNB Sidechain codebase.