With Duolingo users learn a language for free, and simultaneously translate the Web.
Users read, listen to, and translate words and phrases.
They are shown words with translations and can can hear the words pronounced too.
To practice they type and or speak translations.
Activities start out with simple words and phrases and as they become more proficient, Duolingo gives them more challenging phrases.
Duolingo also awards users points and virtual badges.
Before Language practitioners become too anoyed, I want to emphasise Duolingo won't replace in-person instruction, but it is a good site for learners to use to practice writing and speaking a new language. One for ESOL learners as well.