1. Explain it simply
是不是 confirms a guess, like English '..., right?'
It can go before the predicate (你是不是很忙？), at the start (是不是你不知道？), or as a tag at the end (你每天跑步，是不是？).
It already asks a question, so do NOT also add 吗.
2. Show examples
你是不是生病了？
Nǐ shì bu shì shēngbìng le?
You're sick, aren't you?
before the predicate
你今天是不是很忙？
Nǐ jīntiān shì bu shì hěn máng?
You're really busy today, aren't you?
mid-sentence
你每天早上跑步，是不是？
Nǐ měi tiān zǎoshang pǎobù, shì bu shì?
You run every morning, right?
tag at the end
3. Share a tip
是不是 already makes it a question — never add 吗 as well.