Testnet

Testnet is a version of the Stellar network, which is used for development. The network sometimes resets, so the lumens here have no value.

Enable Testnet Feature

Go to main settings (click the “setting” icon on the top right corner of the main menu).
Toggle the switch next to "Show Testnet Accounts" to activate the testnet option.
Select the arrow next to "Settings" to go back to the main page.
Now when you're back on the main page, the button "Switch to Testnet" (on a desktop device) or "Testnet" (on a mobile device) would appear next to the setting button. Select "Switch to Testnet" to go to testnet.
To go back to "mainnet" or to leave testnet, select the "Switch to Mainnet" button next to the setting button.

Friendbot is a tool on the Stellar testnet, which gives you free testnet lumens. Friendly, indeed.