If you haven't already, download Metamask (https://metamask.io/) and create an account. Remember never disclose your seed phrase or password to anyone!
In your Metamask extension widget go to Settings/Networks and click "Add Network"
Paste in the following data:
Network Name:Smart Chain - Testnet
New RPC URL:https://data-seed-prebsc-1-s1.binance.org:8545/