While it’s technically possible to sell items from any station in EVE, the vast majority of items are bought and sold at a small set of stations referred to as “market hubs”. These stations will have literally thousands of times more items available than your average station.
Jita IV - Moon 4 - Caldari Navy Assembly Plant is the most popular market hub. It is located in Caldari space.
Amarr VIII (Oris) - Emperor Family Academy is also fairly popular, and is located in Amarr space.
Dodixie IX - Moon 20 - Federation Navy Assembly Plant is the largest Gallente market hub.
Rens VI - Moon 8 - Brutor Tribe Treasury and
Hek VIII - Moon 12 - Boundless Creation Factory are the largest Minmatar market hubs.
You can visit any of these hubs no matter the race of your character, but your starting system will likely be much closer to the market hubs in your own race’s space.
When traveling to and from a distant trade hub, avoid low-security space. Sometimes the shortest route is through low security space; make sure your autopilot is set to take the safest route instead. Hostile players often camp the “faster” low-security routes between trade hubs in hopes of getting easy kills.