How do you define human needs and their classification by importance and priority of spending, and how is it done?

In Usuli and Fiqhi terminology, needs are divided into necessities (ḍarūriyyāt), needs (ḥājiyyāt), and embellishments (taḥsīniyyāt). Needs (ḥājiyyāt) are those things whose absence leads to hardship, difficulty, and distress for individuals and communities, such as a water heater in bitter cold winter. Their strength and weakness vary according to the need and the hardship one experiences when they are absent.

As for what a person should begin with in spending, its order is as explained by the Prophet, peace be upon him: Spend on yourself, then your wife, then your children, then your servant. This is what Al-Qarafi calls: "A person's entire livelihood, its beginning and completion, is from the necessities in regard to himself, from the needs in regard to his dependents, and from the embellishments in regard to his relatives." The guiding principle in this is moderation in spending, without extravagance or miserliness. Allah, the Almighty, says: (And eat and drink, but be not excessive. Indeed, He likes not those who commit excess) [Al-A'raf: 31], and He says: (And those who, when they spend, do so not excessively nor sparingly but are ever, between that, [justly] moderate) [Al-Furqan: 67], and He says: (And do not make your hand shackled to your neck or extend it completely and [thereby] become blamed and divested) [Al-Isra: 29].