1) when i go to market it says i have 600 gold bar-i dont have a goldsmith
2) when i try to buy or sell them it says i have 0.

Every market may BUY or SELL gold bars.

If it sells gold bars, you will see the number available right below the port production.
To buy these, simply enter the amount you wish and click buy.

i have a noob question to follow up, what can you do with these gold bars?

There are 2 ships in the roster that require gold bars as part of the 'ingredients' to build them. Gold bars can be traded for profit like other port goods. The greatest use of gold Bars is used in construction of Hideout buildings. Be earning 1,000,000 gold coins
( gc)/day before considering hideout buildings.
More uses for GB are forthcoming as the game develops

I just use them as a way to store money if I don't want to have too much in my purse but I don't want to waste turns with banks

Same idea as hoarding iron, which was the top when I started out in avonmora.