Kawaii (かわいい) means “cute”, “sweet” or “lovable”, and in Japan it covers far more than kittens.
A kitten. A lunch box. A pencil case. A grandfather in a knitted hat. In Japan all of these can be かわいい — the word reaches much further than English “cute”.
What it actually means
かわいい means cute, sweet, lovable. You say it about babies and animals, and just as naturally about clothes, stationery, food, handwriting and people of any age. It is a warm word: it says “this makes me feel fond of it”.
On its own, かわいい！ is a complete reaction. It is probably the single most common thing said in a Japanese shop full of small, round things.
The slip to avoid: かわいい and こわい
かわいい is ka-wa-i-i, four beats, with a long い at the end. こわい is ko-wa-i, three beats, and it means “scary”. English speakers often say something between the two. Tell a new mother her baby is こわい and you have said the opposite of what you meant.
みて！ かわいい！
Look! So cute!
ほんとうだ。 かわいいね。
You're right. It is cute.
Making it past or negative
かわいい is an い-adjective, so it changes at the end like おいしい. The course teaches the negative in Chapter 3 and the past in Chapter 8.
Can you use it?
Yes, freely — about things, pets, children and designs. About an adult, use a little care, as you would with “cute” in English: it is friendly between friends, and too familiar for a teacher or a boss. Japanese has other words for good-looking adults, such as きれい (beautiful) and かっこいい (cool, handsome).