XLM (or Lumens) fuels activity on the Stellar network — a system designed to help payments (and currencies) cross borders faster and cheaper than with traditional financial-system networks.
For example, a bank in Japan might use Stellar to send money to a bank in Mexico. Stellar would automatically convert yen to XLM, send the payment via blockchain, and reconvert XLM to pesos at the current exchange rate.
Stellar was intended to work alongside existing assets and cryptocurrencies, allowing users to create digital representations of any asset as a Stellar token. These can then be used to transact on the blockchain, and can be redeemed at any time for the base asset. As an example, a stablecoin pegged to the U.S. dollar, such as USDC, is issued on the Stellar network.
As a decentralized financial network, no single entity can process transactions or stop someone from onboarding or offboarding into Stellar, and the network can still run successfully even if some servers are turned off or fail.