Gold is important in ESO as it allows for repairing gear, increasing inventory and bank space, buying mounts, purchasing equipment from other players, contributing to a guild and upgrading weapons and armor. Making enough gold for all of these things can be a little tricky at first.
If you complete quests, kill monsters and explore the land you will generate enough income to make your way in Tamriel but there are a lot of things that you can do to ensure that you continuously build up a solid pool of gold for which to spend when you reach the higher levels and might want some fancy new armor.
The Justice System is a new way to earn good gold in ESO! You can now, as of Patch 1.6.5, steal from houses and containers and pickpocket the citizens of Tamriel. Stealing and pickpocketing will give you a chance to find different owned items which you can then sell to a Fence for a profit. The items that you can steal vary in quality with base quality items selling for around 50 gold and blue and purple items selling for 300 to 600 gold! You can also find these items by murdering people and looting their corpses.
Be cautious, however, as you will accrue a Bounty from illicit activity and if you are caught by a guard you will be forced to pay your Bounty AND the guard will take your stolen items. If you want to keep a stolen item you can pay a Fence to launder it for you.