Is there anywhere I can read the goddamned 5E rules? The lack of tooltips in this thing is ridiculous.
How does Concentration work? What does Ammunition mean on a bow? Loading on an Xbox?
It was even worst at launch - they've started adding
some info (the stuff you see popping up before the first fight) around patch 3 or 4. Hopefully there will be more.
I normally reference the 5e SRDs (same info, but 2 different layouts):
https://5thsrd.org/
https://roll20.net/compendium/dnd5e/CategoryIndex:Rules#content
Concentration is a new spellcasting mechanic/limitation in 5E. Every character only has a single concentration slot, and it is required to maintain spell effects if indicated by the spell - meaning you can never use two spells that requires concentration simultaneously.
Typically the "stronger" buffs/debuffs/effects require concentration. Stacking buffs/debuffs with a single caster is still possible but now it can't just be anything due to this mechanic. I.e., you cannot have the Haste and Slow spells running at the same time because both spells require your concentration. However, you can have Mage Armor, Haste, and Mirror Image running simultaneously together because only Haste uses your concentration slot in that set of buffs.
Concentration can be lost (spell ends) if you override it with another concentration spell, take damage, or are subjected to a status effect that removes it (i.e. incapacitated/paralyzed). When taking damage, you must make a DC = Damage/2, with 10 as minimum Constitution Saving throw to see if you can maintain the spell. In BG3, it seems like being knocked prone is an auto fail (or a forced save, I don't remember and will need to confirm), but that isn't the case in table top. Not sure if that's a feature or a bug.
In table top, you can voluntarily end your concentration at any time - i.e. dismiss your spell as a free-action, but BG3 has not currently Implemented that yet. So the only way to end a concentration spell prematurely is cast another or take damage, etc.
Ammunition is a property that basically has no effect currently in BG3 - normally in table top that means you need ammo for the weapon to work, but the only ammunition that matters in BG3 is special arrows (think DOS 2 elemental / special arrows). Normal ammunition is not tracked.
Loading on a Xbow is a limitation that currently also has no effect due to the low level limit of EA. It's a property that basically limits Martials to 1 attack per round when they progress to level 5 and get Extra Attack (their version of progressing to BAB +6/+1 in 3.5e/PF)