Just to start off, mabinogi gold is the currency in this game, like it is in many games. Mabinogi Gold is carried as item unlike many games where you can carry a huge amount. So a character is limited how much she can hold in their inventory. You may also store mabinogi money in the bank.
I find this the most efficient way of, making gold at the moment. You basically do runs in dungeons. How does this make money? Well ill use Ciar Beginner Dungeon as a example since its very good for beginners. Ciar Bengginner Dungeon Passes can be first obtained by Ranald, who is located at the School of Tir Chonaill, its free so do not worry. Once you have obtain the pass, just head to Ciar dungeon by taking the Northeast route in Tir and follow it until you get there. You can just spam repeat this over and over since you can get multiple Ciar Beginner Passes and it does not really require much potion use except at Small Golem if you have trouble.