Unlike most MMORPGs, ESO does not have an auction house system (or a central location for buying and selling). Instead, it's broken up into a couple of dozen kiosks scattered across all the regions of the map. Some are in higher traffic areas, making them more desirable locations. Higher traffic means that more people are likely to visit that kiosk and buy from it. To get a kiosk, you'll need to be in a guild with at least 50 members and bid blind on a spot weekly using gold. The more desirable areas can cost guilds up to 4-7mil gold per week! In order to generate that kind of revenue, guilds usually have to require a guild membership fee and run a variety of fundraisers, usually in the form of 50/50 raffles (half of proceedings go to winner and half to the guild).
When starting out, you might want to look for a free guild trader guild. They typically have less than ideal locations, but you'll likely not have very many things to sell at the beginning, making for a good fit.