okay so I haven't looked for help in the game on combat or anything because at first glance its so similar to the original Xenoblade Chronicles. But the whole "green circle fills up to make it more powerful" was new to me, anything else I should know about combat? Or is there some tutorial I should know?
First thing you should know is that Blast Fencer's Essence Exchange is OP. Start every fight with full TP (well it will be full if you have a minimum of 3000 HP). Other classes have their own ways of building TP fast. When you max out a class line (get the rightmost class in the line to rank 10) you will unlock its weapons so they can be used on any other class.
Since all artes are tied to weapons that means when you have some classes maxed out you can go to the Drifter class (the one you start with) and create your own custom class. The reason you go to Drifter for this is because it has the most Skill slots IIRC.
Overdrive (chapter 5 unlock) uses 3000 TP to put you into a super mode where all of your abilities recharge faster and you gain access to tertiary cooldown (white ring that fills around artes after the green ring (secondary cooldown) has filled). You can check their effects in the artes menu but it's mostly stuff like +250/+400% damage increase for waiting for the secondary/tertiary cooldowns.
Artes have different colours, like range is usually yellow, melee usually orange, auras are usually blue, recovery/buff artes are usually green and status effect/debuff artes are usually purple. Depending on how you chain these colours together will give you different bonuses in Overdrive.
When something says "+100% damage when used in a melee combo" they mean that you need to use the arte AFTER a melee arte.
Using a melee arte first makes it a melee combo to the arte you use after.
So [Use Melee Arte --> Use Arte that gains bonus from being used in melee combo].
Same goes for range.
Might add more later.