

昨日は雨でした。
昨日、何を食べましたか。
昨日は学校に行きませんでした。
"きのう(昨日)" is in the lesson "Time 2" (Level 35), along with 11 other useful words. LinDuo has 180 topic lessons like this one, 2,379 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.