The Trader and the two Dealers all have exchange screens. In these, your bargaining items are on the left of the screen, the trader's stock is on the right, and the center of the screen is devoted to the currently selected item.
The Launch Pad is the location of your ship. It is represented by a landing-pad or a skyline icon. It has two options: Launch to Space and (if your ship is damaged) Ship Repair. The Ship Repair option pulls you over to the Equipment Dealer's screen.
The Equipment Dealer, Commodity Trader and Ship Dealer characters may be visible from the launchpad. Clicking on them will take you to their respective screens.
The Bar is the place to make connections, pick up missions, and catch up on the news. It is represented by a foaming mug icon. It has two sub-buttons: Job Board (a briefcase) and News (a newspaper). The bar itself is a large room with a big window, populated with a bartender and two to eight patrons. The patrons change if you leave the Bar; visit several times to make sure you've met them all.
The Job Board lets you pick a mission to do. It lists the mission giver, mission type, difficulty and pay. Selecting one brings up a description, which spells out the target, location and whether you will have backup. If you like what you see, click the Accept Job button and get cracking.
The News brings up the local Colony News Service feed, which includes World news (globe icon), System news (solar system icon), Universe news (starfield icon) and Faction news (flag icon). During story mode, it also has Mission-Critical news (exclamation point icon). Checking the news does not directly benefit you, but it provides interesting fluff about the Freelancer universe. Note that some of the most far-flung outposts don't get CNS service and will not have a News icon.
The patrons and bartender may have interesting things to say; float your cursor over them to see. Talking to a bar denizen has a short cinematic for exchanging greetings,but you can hit Esc to skip this.
A briefcase icon means they have a job for you; this works exactly like the Job Board, except for the specific missions offered.
A circled 'i' means they are offering to sell you the location of an object in space, which could be a Wreck, a Jump Hole or the complete readout for a Base. Buying the information uploads it directly to your Navmap. This is usually not worth the money. Everything except Wrecks can be found using your navmap's Show Patrol Routes feature and a little patient detective work, and if they offer you a wreck the teaser alone gives you a rough idea of where it is.
A dollar sign means they are a bribe carrier, offering you a way to buy off an enemy faction. This will anger the target faction's enemies, but still may be the best choice if other methods of improvement are too much bother. This is mostly useful to freighter Traders, whose main priority is to have as few enemies as possible along their preferred route.
An empty speech bubble means that the character's faction is hostile to you, and if you approach them they will angrily tell you to get lost. Alternatively, they may be a bribe carrier whose target faction is already friendly to you.
The Trader and Dealer rooms may include extra characters who have the same functions as the bar-goers. This usually only happens on major planets.
The Commodity Trader is where you buy and sell Commodities. Their icon is a stack of boxes. Talking to the trader character brings up the exchange screen.
The exchange screen shows colored lights for each Commodity. Green means this is a good place to (sell your/buy their) stock of the commodity, yellow means average price, and red warns you of a bad deal.
If you just sold the trader a commodity they do not stock, the stuff you sold will appear on their side in case you want to buy it back. For any given base, each commodity will command the same price whether you're buying or selling.
The Equipment Dealer is where you buy new weapons and stock up on munitions for your ship. They are represented by a cogwheel icon. This has three sub-buttons: Dealer, Change View and Ship Repair (if the ship is damaged).
Talking to the character brings up the exchange screen, which has four different subscreens for weapons (gun icon), ammo (bullets icon), equipment (cogwheel icon), and nanobots/shield batteries (cogwheel-inside-ship icon). Your weapons and equipment will show a Mount/Unmount button, which you can use to install new loot or switch between different loadouts.
Munitions, bots and batteries cost the same whether buying or selling, but you can only sell your weapons and equipment for a fraction of the buying price. If you make a trade, until you leave the station you retain the option of reversing said trade without losing money. Weapons on offer will be a limited selection of whatever the base owners use, plus some Civilian Weapons.
You can only buy new weapons if you're high enough level, are friendly enough for the station owners to trust you with extra weaponry, and have a free hardpoint on the ship. In some cases, you may need to vacate a hardpoint to buy a new weapon, even if you only wanted a spare.
The Ship Dealer is where you buy new ships. It is represented by a vertical ship icon. The Dealer will have one to three ships available, assuming there even is a Dealer; this is to only location that is commonly missing from a base.
The Exchange screen will lead to a second screen, a combination of the Equipment dealer and Commodity Trader screens, where you can change the loadout on your new ship and bargain your stuff to the dealer to lower the credit price. The listed price includes a Shield and a basic Thruster; if you're satisfied with the ones you have, you can save money by giving the default ones back.
The purchase is not final until you click the Complete button; if you back out without doing so, the whole trade is cancelled. This means you can check out offered ships and even compare your inventory to their loadouts at no risk to you.