The purpose of fusing is to create a higher tier hero, which will increase health, damage, and daily earning potential for that hero.
Higher tier heroes will be more rare as you need to burn 2 lower tier heroes in order to create the higher tier hero. The fusing process will also cost tokens in order to complete. Tokens from fusing will be burned.
You will need to use 2 of the same heroes to successfully fuse. For example, you will need 2 Knights of the same tier in order to mint a Knight with a higher tier.
Fusing will look like this:
2 tier 1 heroes of the same class are needed in order to fuse and mint a hero with tier 2 ranking.
If you fuse 2 Magicians with tier 1 rankings, you will mint a tier 2 Magician upon successful fusing.
2 tier 2 heroes of the same class are needed in order to fuse and mint a hero with tier 3 ranking.
If you fuse 2 Druids with tier 2 rankings, you will mint a tier 3 Druid upon successful fusing.