1. Explain it simply
如果 introduces a condition; 就 introduces the result: 如果 …，就 …。
如果 goes at the start of the first clause; 就 goes right before the verb in the second.
You can add 的话 after the condition: 如果明天下雨的话，我就不去了。
2. Show examples
如果明天下雨，我就不去了。
Rúguǒ míngtiān xiàyǔ, wǒ jiù bù qù le.
Sandhi:Rúguǒ míngtiān xiàyǔ, wǒ jiù bú qù le.
If it rains tomorrow, I won't go.
condition then result
如果你累了，就休息一下。
Rúguǒ nǐ lèi le, jiù xiūxi yīxià.
Sandhi:Rúguǒ nǐ lèi le, jiù xiūxi yíxià.
If you're tired, rest a bit.
就 before the verb
如果有时间，我就去看电影。
Rúguǒ yǒu shíjiān, wǒ jiù qù kàn diànyǐng.
If I have time, I'll go see a movie.
如果 …, 就 …
3. Share a tip
就 stays inside the result clause, right before the verb - never put 如果 or 就 at the end.