If you are using these Elements, you need a Mercenary or party members that can deal with them. In Hell difficulty you'll face monsters that are Immune to Cold and monsters that are Immune to Fire.
Akara rewards you with an additional Skill Point and the ability to Reset your Stats and Skill Points, once per difficulty. The objective of this Quest is to kill every monster in the Den of Evil which is located in Blood Moor just outside the Rogue Encampment in Act 1. Completing these Important Quests in all 3 difficulties results in a total of 12 Skill Points which greatly increase the power of your Characters. There are 3 Quests that permanently grant your Character additional Skill Points. The remaining 15 Quests are side Quests with varying degrees of importance.
Out of the 27 Quests, 12 Quests must be completed to progress through the game. In Diablo 2 Resurrected there are specific Important Quests that every Character should complete to increase their power.