Short Answer 
To customize vehicles in the game, first, acquire a Mobile Operations Center (MOC) with a Vehicle Workshop module from Warstock Cache & Carry. Then, drive the vehicle into the MOC, access the customization menu, and personalize it according to your preferences and in-game requirements.
Step 1: Acquire the Mobile Operations Center
To begin, you need to purchase and customize your own Mobile Operations Center (MOC) from Warstock Cache & Carry. Ensure that it has the necessary features to operate effectively, especially the Vehicle Workshop module, which is crucial for vehicle modifications. This step sets the foundation for your customization journey.
Step 2: Access the Vehicle Workshop
After securing the MOC, you can start modifying your vehicles. First, drive the vehicle you intend to modify into the back of the MOC. Then, access the vehicle customization menu by pressing the relevant button, usually the right D-pad if you’re using a console. This menu allows you to explore various modification options available for your vehicle.
Step 3: Customize Your Vehicle
Now that you’re in the customization menu, you can personalize your vehicle based on your preferences and budget. Options may include weapon upgrades, aesthetic changes, or performance enhancements. Keep in mind that certain modifications might require you to complete specific missions or achieve certain ranks within the game to unlock all available features.