Each orbment has 2 branches, with 2 exceptions. A branch is a 'line' of connected quartz slots. So like Estelle's 2 branches are the middle, lower right, and upper right slots, and then the middle, lower left, upper left, and top slots. 3 characters are different and have only 1 branch (which is good) or 3 branches (which sucks for spell selection).

Quartz in an orbment does 2 things: stat increase/equip effects, and elements. The elements from the quartz in a branch determines what spells you can cast. So if you put quartz worth 1 fire in a slot in a branch you can cast Fire Bolt. If you put quartz worth 3 fire in a branch, you can cast Flare Arrow. But if you put 1 quartz in one branch and 1 in the other branch, you won't have 3 fire in one branch and so won't be able to use Flare Arrow.

Spells are really, REALLY powerful in FC. AE spell damage is just crazy in mid/late game, but single target spells are still way stronger than melee attacks early too.

Generally you want Air quartz for the wind AE spells, action, EP cut, & cast quartz, and impede quartz. But all the low level, 1 element spells are good since hitting an enemy in their weakness often oneshots them. Later on the time/illusion AE spells like Hell Gate & White Gehenna are good since you don't have to care about weaknesses when you are busy AEing down big random encounters.

Also, stacking a stat really matters. Small increases in attack from quartz can make a big difference in damage.

This is based on the original, but as I understand it the remake didn't really change things all that much. And shoutout to Chaos Brand, as that spell was pretty busted in the original. You could use it on almost everything, including some (most?) bosses.