

Кто-то звонит в дверь.
Someone is ringing the doorbell.
Тут кто-то есть?
Is anyone here?
Кто-то взял мою ручку.
Someone took my pen.
"кто-то" is in the lesson "Pronouns" (Level 30), along with 17 other useful words. LinDuo has 180 topic lessons like this one, 2,380 words in total. Every word has an illustration, a transcription and pronunciation in a female and a male voice. Just 10–15 minutes a day is enough to learn them all. Free, and works offline.