Both Ethereum Mainnet and Ethereum Ropsten networks use identical technology and software. The main difference between the two is that the Mainnet network is used for 'actual' transactions with real monetary value, whereas the Ropsten network is used for 'testing' smart contracts and decentralized applications called DApps. The Ethereum Ropsten network is essentially a simulation of the Ethereum Mainnet.
Ethereum Mainnet: - Transactions performed using Ether which holds monetary value - Tradable, exchangeable on public exchanges e.g. Coinbase - Used for transactions with monetary value - Transactions incur fees in Ether - 'Proof of Work' consensus, minable - Network ID = 1
Ethereum Ropsten: - Transactions performed using Test Ether which does not hold monetary value - Not tradable, or exchangeable on public exchanges e.g. Coinbase - Transactions incur fees in Test Ether - 'Proof of Work' consensus, minable - Network ID ≠ 1
If you want to know more about the difference between the two networks, see this Medium article.