Throughout the game you will collect, enchant, combine and equip newer and better gear. Each piece of equipment contributes to one of four stats that affects your gameplay in positive ways. Without this equipment all your stats except your Hero HP would be zero.
This stat is one of the more noticeable of the four and can be observed simply by looking at the number in the little red tear at the feet of your hero whenever you're in a match. This number represents how much health your hero has and how much you can lose before you die and, therefore, are defeated. You cannot regain this health once a match has started but it does reset to its full capacity between every match and no extra steps are needed to heal yourself.
There is only one way to gain more health but there are multiple items that can do so. The first item you'll be able to get, and the highest stat increase, will be Armor. The other item is a Ring of Life, or some other "of Life" item, which increases your Hero HP by a minimal amount. You can also purchase mounts which may or may not increase this particular stat and will not increase it by much.
The armor can be obtained by defeating the boss Sanguine Tribe (normal or hard, although hard gives you better armor) and the "of life" items are unknown.
This stat affects how often you crit while using direct attack skill cards like Slash, True Shot, Fireball or Smite, among others. Criting, or critical strike, causes you to do double damage every once in awhile. Increasing this stat will increase the frequency of which you deal critical strikes.
Like Hero HP, there's only a few ways to increase this stat. One, by farming the boss Shimmering Cave (easy, normal or hard) and hoping to get lucky with your picks or, two, by purchasing a mount. You can also get an "of Wisdom" item which can be obtained by defeating Desert Fortress and increases your Hero Crit by a minimal amount.
This stat doesn't directly affect your hero like the first two but is just as important, if not more important. This stat affects how often your units crit, simply put. On occasion they will deal double damage, or sometimes even 4 times the damage! The more this stat is increased, the more frequently they will crit.
The main way to increase this stat is by farming for a Weapon from Windy Cliff, or by equipping a mount and a "of Bravery" item.
The final stat is like the opposite of Unit Crit. Unit Block causes your units to occasionally block for half the damage they normally would have received. When on the defensive or even when you're the aggressor, this stat can be very valuable with just a little luck on your side.
The main piece of equipment to get to increase this stat is the Cloak, which can be obtained by defeating the boss Dark Forest. Mounts and "of Perseverance" items, dropped by the boss Castle of Bones, can also increase this stat.