需 demand

I demand your Juicy Underwear!

My hair got wet in the rain and I demand to receive a comb.

demand ★★☆☆☆ NP
需 (demand) + 要 (important) = 需要 (demand)

demand in the economic sense - supply and demand

This does NOT get to turn into a verb. You don't use する. You'd say 需要がある (there's a demand for xxx) or perhaps　　需要を　満たす　（じゅようをもたす） (there's enough of xxx to meet the demand).

necessities ☆☆☆☆☆
必 (surely) + 需 (demand) + 品 (products) = 必需品 (necessities)

necessities: both on everyday occasions and on adventures. Like if you're leaving the house you need your keitai and your keys! But also if you're going to the moon you need your ray gun and your moon bikini.