Red Dead Redemption 2 isn't a game that is very forthcoming with explanations of its systems. As a result, some mechanics might be harder to get the hang of early on.
Your core stats, three of the five orbs above your mini-map, denote Health, Stamina and Dead-Eye. Charging these, and more importantly upgrading them, isn't well explained, nor is the difference between cores and bars. This guide will help you out with these stats.
Note that the other two cores (to make the total of five) are horse health and stamina, which aren't as important as the others.
Cores Versus Bars
With cores, you have two values, one is the "bar" which is actually the colored fill around the edge of the circle and the other is the core (inner part) itself. Cores are Rockstar's way of adding a measure of survival gameplay to Red Dead Redemption 2. The main difference between cores and bars is that cores drain passively.
Not doing anything, not using anything, not touching the controller - your cores still drain. The health and stamina cores work the same way, but Dead-Eye is different, so we'll deal with that later on.
Basically, core drain is Rockstar's abstraction of hunger, fatigue, discomfort and so on. If you don't eat for a long time, the cores drain quicker. If you are dressed for the wrong weather, your cores will drain quicker.
In ideal circumstances, meaning there are no extra factors causing Arthur problems, cores drain from full to empty in 90 real-world minutes (this still applies to Dead-Eye).
Bars, on the other hand, work like health and stamina does in every other game. Get shot, health bar goes down. Sprint, stamina bar goes down.
Bars Depend On Your Cores
How are bars and cores related? Simple - the more juice in your Health and Stamina cores, the faster your bars regenerate. If your cores are running low, regeneration takes a hit.
Another interaction is that when the bars run out, the cores start being consumed. If you take so much damage that your health bar is empty, Arthur doesn't die immediately, but rather further damage reduces your health core. When both are empty, you're wasted.
Refilling Cores and Bars
In practical terms, this means that so long as you don't empty your bars in any circumstances, you only need to care about cores every good hour or so.
In order to refill cores and bars, the game uses a wide array of consumable items, which are helpfully categorized. All Provisions refill cores, with their description stating which core they refill, while Tonics refill bars.
Alternatively, resting can refill cores. Take Arthur back to camp, or to any bed you encounter that isn't occupied, and take a nap.
Certain Tonics have yellow icons. This means that they don't only refill one of your bars, but fortify them. Fortified bars turn yellow and for a short amount of time do not drain even when used. Think of these as special potions are used in other games - you typically use them when you know a tough encounter is ahead.
Cores are un-upgradeable. All cores drain from full to empty in 90 minutes and there is nothing you can do about that.
Bars are a different story. Bars have their own system for upgrades where using them upgrades them in a sense. Running or performing other Stamina consuming activities will, over time, upgrade your Stamina bar. Shooting enemies or animals with Dead-Eye will upgrade it. Skinning animals and gathering food upgrades Health.
Dead-Eye Core and Bar
While the Dead-Eye core is the same, the Dead-Eye bar isn't - it doesn't regenerate.
Even at a full core, you need to manually refill Dead-Eye's bar with Tonics. Additionally, there is a percentage chance to get a small instant Dead-Eye refill whenever you score a kill.
Horse Cores and Bars
Horse cores and bars are also upgraded through use and refilled with Provisions and Tonics. However, you can also upgrade bars by bonding with your horse through praise and grooming, and these acts will also help keep core drain at a minimum.
You can check out our beginner's guide here.