There are various items which can be bought in the shop spread over tabs;
Here you can see what you ordered, and the house and cars you bought.
Here you can buy weapons, weapons give you a higher chance to kill other players. Remember you can only have 1 handgun and 1 tommy gun.
Remember after a MOC, you will lose your weapons. You can also buy special weapons like Molotov cocktails, after a kill attempt you will lose these.
Special weapons are automatically used when you attack someone else. Grenades are used in every attempt and will increase your attack.
Molotov cocktails are used when you attack an online target. They add attack and can destroy your victim's transport.
C4 is used when you attack an offline target that owns a villa. If you carry enough C4 these villa will be destroyed
Here you can buy a vest or suit to protect yourself against kill attempts. Armour adds defense to increase your chance to survive an attack by another player.
You can own either a vest or a full suit. Both can be destroyed in a kill attempt.
Transport gives you extra protection against kill attempts, and also gives you a bonus when you attack other players. Remember you can have only 1 transport vehicle per city.
Your cars will only protect you when you are online.
Planes allow you to travel across the continents and access cities you can not visit by train, they can also lower your travel time. A plane is needed to travel between the 2 continents.
This way you will be able to fly from Italy to the USA and the other way around. Also the more expensive your plane is, the less waiting time you will have between traveling.
So when you have the most expensive plane, you will be able to make more money smuggling.
Here you can buy and train bodyguards. Every bodyguard has his own specialty. It's wise to over think who you hire to get the perfect balance in what specialties you find important.
You can read more about bodyguards here.