Amber is a type of currency that is used to acquire cards in a match. They drop from Minions, Neutral Monsters, and Heroes when they die and can also be obtained with Harvesters at specific points on the map. Amber also contributes towards a player's card experience (CXP). Leveling cards grants the player card points that can be spent on new cards.
One thing that's unique to Paragon is all amber received by a player is split among all nearby players. While one nearby player receives the same amount of amber as the original player, any additional nearby players will cause the amount to split more. See the guide below.
Before update .27, all nearby players received the full amount of amber that the original player received. That mechanic was adjusted because it encouraged the "deathball" strategy, which made grouping up and ganging up on isolated heroes the most effective way for a team to gain amber.