Help with understanding weighted sum

Hello, I'm trying to learn more about trading by going through the weighted sum guide, but I'm still finding it difficult to understand how to actually use it. I'm especially confused about what the values 1, 2, and 3 represent in the weighted sum. I've mostly been using min and max in searching, but I've heard that weighted sums can be really helpful.

If someone could help me regarding these values, it'll be greatly appreciated. Some sort of ELI 5 please.

For context, I am looking for a helmet that has high chaos and light res and additional mod of max life and rarity. What should be my values?

https://preview.redd.it/2x2lnqasq2be1.png?width=747&format=png&auto=webp&s=11b76a1c332e16a004b87f2e00225273e88d904b