Direct interactions with other players does not seem to be an active part of the game. However, the market seems to be entirely run off of player characters. The prices fluctuate and generally follow supply and demand. This reminds me of Runescape which is a game I played quite often growing up. I’m not sure if that game was an inspiration or not, but if it worked for Runescape, I can understand why it works for Black Desert Online. The central market is still very intimidating and hard for me to understand. This is most likely because of the interface, which seems more complex than what I am used to.
Your guide is called the black spirit and is involved in the plot of the game. The black spirit gives you quests, but you can also find quests by talking to NPCs. I find the black spirit to be an interesting character because when I first met them I thought they were very creepy, which I believe is the point. The developers want the player to be unsure if they can trust this character and I see a likely betrayal coming in the future.
You can buy houses, which can be used to store things. This still confuses me a bit, but this is likely because of the larger gaps of time being playing and not paying enough attention to dialogue. It is simple enough to Google something that is unclear and there is an online forum community, whether through the official site, Steam, Reddit, or another website.
The map seems to be huge. I have yet to explore it all and it seems very dangerous to attempt to at my current level. With aggressive enemies near the roads that are likely at a much higher level than I can handle, I will most likely have to continue to discover the map as I level up. There are bosses that can be fought and this can be done solo or with a party. I really enjoyed this part thus far, especially when I had a party with me.