Where the money is
Your gold sits in the footer of your bags, next to how much you are carrying. Press I and it is there.
It comes from people who ask you to do things for them. Rennick pays for the crows, and every monster pays something. What it buys is gear from the shops in Aeven, more room at the bank, and one day a guild of your own.
Everything takes up room
A bag is not a list. A bow takes more space than a ring, and things sit in the grid at the size they actually are, so what you can carry is a real decision rather than a counter. Weight matters too: load yourself up and you will feel it.
You have three bags. When they are full, you have a choice to make, and that is where the bank comes in.
The bank
Bank Daddy keeps the Aeven Bank. Your first drawer costs nothing, the bank does not care what things weigh, and what you leave there stays there whatever happens to what you are carrying. More drawers cost gold, and they are the main reason to hold on to money rather than spend it as it arrives. The whole of it is in the bank.
What to keep and what to drop
Keep anything you cannot get again easily. Drop, or leave on the floor, anything you are carrying out of habit. The floor is a real place: what you put down stays there for a while, so you can go back for it if you change your mind.
Passing things on
Stand next to a friend and open a trade to hand them items or coin directly, or post it to them from the mailman and it waits until they next sign in.
More on what there is to spend money on: quests and dungeons.