Most items in game are player made. With the fact you can't repair items and that you will die and lose everything eventually, this creates a healthy player economy. Never carry around what you can’t afford to lose (this is worth mentioning many times) and if possible always have some reserves in the city you're currently stationed. Keep bringing what you get to bank often, don’t be too greedy. And when you are going to change the city you work in, bring with you only what you need.

Bank, mail, stables and broker are all local, meaning what you have in one city's bank, you can’t access from another city and what you’re selling on one city’s broker can’t be bought in another city. You can’t send items to another city by mail and you can’t access your pets in other stables, only those that you stabled your pet in. This means, that whenever you change city you basically start from scratch. This is also the most dangerous thing to do in MO, moving your hard earned items from one city to another. This is why it’s important to have supplies in many cities, so you can travel light and in case of death you lose very little.

Why would you change city you might ask? Because the world is big, and with no way of fast traveling and sending goods around, you might want to move around from city to city depending on what your current thing you’re doing is. Let’s say you live in Morin Khur as a miner, and want to start mining Suburra. Your only choice is to go to Tindrem or Meduli, since this is where Suburra can be found. It would be too dangerous to mine there and haul everything back to Morin Khur. It’s safer to station yourself near the place you currently work. Gerring basic money to jumpstart your operation is quite easy, even if you get to a new city naked. All you need is to pick couple of flowers or plants, sell for basic weapon or tool and work from there on.

So far I covered that most items are player made, but there are some useful items that can be bought from vendors. There are various NPCs that offer their services, so let me describe them a bit:

Bank - Each town has its own bank which is completely separate to all other town banks, ie stuff stored in 1 bank will not be retrievable from another town. All banks are 100 slots but only have 50 slots visible, to use the other 50 you must use bags. Players can also create banks but be warned, player made banks are vulnerable to being destroyed and your stuff will be lost.

Mail - A NPC called Veredari serves as a mail in MO. You can send items within the same city to other players (also your alts if you have them). When sending you have the option to send with cash on delivery (COD), which means receiver must pay for items to get them. Each item you sell will cost you 1 silver (whole stack is considered one item). Careful when you take items out, if you press the “receive all” button and you get more items than you can carry, you won’t be able to move. This means you will need a friend, pet with bags or will have to destroy/drop items to be able to move again. Only take out of mail what you can carry and keep an eye out for suspicious players that might be thieves.

Stables - The role of stables is done by NPC called Equerry. Here you can stable your pet for a fee of 1 silver. You can put your pets to train of if you have a male and female mount you can breed them to get better mounts. You can stable up to 5 pets in one stable without Management skill, but there are usually many stables around, so you can have more pets in each city if you really need it. There is also an option to create a receipt for your pet, which can be sold on broker or send by mail if you want to sell your pets to other players (you can also transfer pet directly for free) and it will cost you 50 silver to make. Also if you buy a pet, you can turn the receipt in at stables to get the animal you bought, but you must turn it in at the same stables that this animal is stabled (it says on it which stable it’s for). Careful when carrying receipts, they can be easily stolen.

Broker - Broker can most of the time be found near banker. Here you can sell and buy items put on broker by other players. First tab will help you search for items on the broker (keep in mind you can only buy items on broker in the same city, altho you can search for other cities). If there is a “bag” icon next to the item, you can click it and see what items you get for buying it. This is mostly used for armor sets.
The second tab is Buy Orders, where players can put in what they are buying, and you can fill those orders (completely or partially) and earning what is offered. This could be described as some sort of player made quests and most things you see there are materials others need.
Third tab is for selling items on broker. You set a price, pay 10% fee and set how long the item will be listed. If you sell an item you will get your money by mail in the same city.

Library - There are many different librarians in cities, and they sell skill books.
Tindremic/Khurite librarian - Sells basic books, for most skills you need at start, like combat, weapons, gathering, crafting, etc…
Petrologist librarian - Sells books for material lores you need when mining.
Crafting librarian - Sells books for crafting, some can be found at tindremic librarian, but is more specialized
Animist librarian - Sells books that are focused more for tamers and mages
Zoology librarian - One of the biggest skill tree is zoology, you can find all sort of lore about creatures that inhabit MO world. To be successful at taming, butchering and to some degree fighting them, you need knowledge about them. This is where you get books for them if you don’t want to train it up manually. There is only (as far as I know) one zoologist in the game, he’s in wilderness in Vadda valley and can be quite dangerous to go there with bags full of gold, so be carefull.
Other book vendors - There are many other librarians out in the world that sell more rare books and usually don’t take gold as payment. Those are not necessary for beginners so I’ll skip them from this guide. There are enough resources on internet if you search for them (hint: Mortal Online book list) and if you’re gonna stick around in MO you need to do some research on your own anyway.

Vendors - For last this is a short list of vendors and some useful items they sell
Food vendor - Sells some basic food, mostly used for buying “dile” that can be cooked with 10.000 water which makes cheap mount food.
Utility vendor - Sells some useful items like Torch, Campfire, Mining axe, Bandages and starter weapons
Reagent vendor - Sells basic reagents needed for magic spells and some other professions
Gear vendor - Sells basic gear for adventuring like portable workbenches

I would like to mention Tindremic and Kallardian armor vendors found in starter cities. They sell Tindremic Scale and Kallardian Padded armor for 1.35 gold (for whole set), which is a good starting armor if you can’t get a cheap one from players. You should be able to get better and cheaper armor from players tho, but I like to mention them just so you have the option of quickly gearing yourself. Also if you can’t get a cheap player made weapon, you can buy one from gear vendor or "Arx Meridius" (he only takes undead heads as payment). Basic weapons (a bit better than worn) can be bought for 20 silver and exceptional version for 1 gold, but they are still worse than most player made weapons.