Almost all rolls in Savage Worlds are performed with exploding dice. Exploding dice are dice that, when the maximum is rolled, the dice is rerolled and added to the number. Dice may explode infinitely in Savage Worlds.
When rolling, you are generally trying to meet or exceed a Target Number (TN). Most of of the time, this TN is set at 4. Notable exceptions are Fighting rolls, which uses the target's Parry score, and damage rolls, which use the target's Toughness score. Opposed rolls use the defender's (if one can be determined) roll to set a TN which the attacker must exceed.
If the roll exceeds the TN by 4 or more, it is considered a raise. For every 4 you exceed, another raise is obtained, indicating your degree of success.