The main Free TON network is main.ton.dev

The main network is available in Surf. You can purchase Crystals in Surf: Surf main page -> Top up.

The test network or devnet as we call it, is net.ton.dev with Rubies test coins.

Devnet runs the latest stable version of the Free TON Blockchain. The goal of the devnet is to provide a stable development environment for application developers. It is optimized to connect with TON Labs SDK. Read more here: https://docs.ton.dev

You can easily switch between the networks in Surf: SettingsAdvanced settingsDeveloper mode.

Please note that your Surf address is the same for mainnet and the devnet; however, the address for mainnet cannot be deployed while your TON Crystals balance is zero.