Lumens are the ‘native assets’ of the Stellar network. Stellar is a somewhat different blockchain protocol than other cryptocurrencies, and often draws comparisons to Ripple. Like XRP, Lumens are digital tokens designed to help dissolve inefficiencies among financial institutions and consumers.
The best way to start conceptualizing Stellar is to imagine how Venmo works today. You upload money and have access to it right away. When you transfer it, you do so easily and instantly (and pending it’s through your debit card, free). If Stellar succeeds, it will create a similar system, but on a global scale—and for larger bodies like banks and corporations.
In a practical sense, this means that you could pay your friend in Mexico with XLM and that friend could withdraw the money in pesos. Or, if you were traveling abroad, you could use XLM to pay without ever going through the process of converting your money to a foreign currency.