Your skill menu is located in the F2 menu. While doing an activity in that category, buying a gym membership or doing civ jobs, you’ll gain points in that skill. Once you reach a certain level in a skill, you’ll gain an extension in that skill or unlock new things to make.
Stamina – How long you can run.
Strength – How much you can carry in your inventory.
Diving – How long you can hold your breath underwater.
Mechanical – Parts/Upgrades you can make for vehicles
Engineering – Coming Soon
Drugs – Kinds of drugs you can make
Hacking – Coming Soon
Theft – Coming Soon