1. Explain it simply
要是 (yàoshi) means 'if'; it is the colloquial, everyday version of 如果.
Word order: 要是 + condition + comma + subject + 就 + result.
就 comes AFTER the subject of the second clause and right before its verb, not at the head of the sentence.
要是 opens the condition and 就 points to the result - do not stack them together or drop the 就.
2. Show examples
要是明天天气好，我们就去爬山。
Yàoshi míngtiān tiānqì hǎo, wǒmen jiù qù páshān.
If the weather is nice tomorrow, we'll go hiking.
要是 sets up the condition
要是你有时间，就来我家玩。
Yàoshi nǐ yǒu shíjiān, jiù lái wǒ jiā wán.
If you have time, come over to my house.
就 introduces the result
要是他累了，就在家休息。
Yàoshi tā lèi le, jiù zài jiā xiūxi.
If he's tired, he'll rest at home.
就 sits before the verb
3. Share a tip
就 is not a sentence starter - keep it right before the verb of the result clause, as in 我们就去, never 就我们去.