If you’re interested in contract audit/security: Ethernaut is a good resource. Connect Metamask and Rinkbey test-net. Play a game by connecting your Rinkbey wallet on Metamask:

• open Ethernaut then open developer console: console
• type the following commands:
  • player
  • getBalance(player) or await getBalance(player)
  • ethernaut.owner()
  • contract.method7123949
  • contract.password
  • password.authenticate
  • contract.authenticate("METAMASK PASSWORD")
  • contract.infoNum(). then(v => v. toString())

Testnet setups

• Rinkbey setup on Metamask
• Metamask wallet testnets setup
  • name
  • rpc link
  • chain ID
• Network and Chain ID - Testnet