Mana is the resource that players use to cast non-item cards. Each tower has its own mana pool that can be spent or modified independently from other towers. At the start of each round, each tower's mana pool is replenished and increased by 1.
Cards are the essential element of Artifact that players use to interact with the game. Cards can take the form of Creeps, Spells, Improvements, and Items. By default, players start with 5 cards and draw 2 more at the start of each round.
Improvements apply some sort of continuous effect to a lane permanently, unless/until they are destroyed by the opponent. Due to their nature, improvements often have the potential to snowball a lane out of control over time.
Equipment items are bought from the Shop at the cost of gold and generally serve to increase a hero's Attack, Armor, or Health. Some items bestow additional powerful special effects or abilities. Consumable items are single-use only, and allow the player to heal a unit, teleport a hero, or draw an additional card.
Unblocked units select a random combat target at the start of the round or when newly spawning in to the battlefield. Units have a 2/4 chance to attack the tower, 1/4 to curve left, and 1/4 to curve right. If there is no unit there when the attack curves, the unit will attack the tower.
Most attacks and effects in the game deal Normal Damage, which get reduced by positive armor and amplified by negative armor. Piercing Damage is special in that it ignores positive armor, but still benefits from negative armor.
All heroes and creeps have the three primary stats, though armor is simply unlisted when a unit has zero innate armor. Attack refers to how much damage the unit deals to its target in combat, Armor reduces each incoming damage instance by that amount, and Health refers to a unit's life total -- if it is reduced to 0, the unit dies.
Bounty defines how much Gold a player receives for the death of an enemy unit -- by default, this value is 1g for creeps, and 5g for heroes. Bounty is awarded on-death, and does not depend on how a unit dies or which player killed it.
Allied Neighbors = allies directly adjacent to the unit, on its left and right. Enemy Neighbors = the enemy units occupying the slots diagonally left, directly across, and diagonally right from the unit.