How Do You Use a Japanese to English Dictionary?

In Japanese, you had to look for the word and then stick it on an anti-card. In Mandarin, because there's a tonal language also, you're not entirely sure which tone they're using on certain words. So I would kind of, when I was like reading comic books or watching a TV show, I'd be kind of like hunting for these sentences. Where I understand everything but one word. And that way I can like use the sentence to teach myself the word.