Used to introduce a topic: 'speaking of...' — brings up something related to what was just mentioned.
日本といえば寿司や桜を思い浮かべる人が多い。
Speaking of Japan, many people think of sushi and cherry blossoms.
夏といえば海や花火が定番だ。
Speaking of summer, the beach and fireworks are typical.
その店といえば、昔から人気がありますね。
Speaking of that shop, it's been popular for a long time, hasn't it?
Used like 'when it comes to...' or 'as for ...' to narrow the subject and make a comment or comparison about it.
車といえば、燃費も重要だ。
When it comes to cars, fuel economy is also important.
試験といえば、去年より難しかったらしい。
As for the exam, it seems it was harder than last year.
旅行といえば写真をたくさん撮る。
When it comes to travelling, I take lots of photos.