Skills are unlocked in F.I.S.T Forged in Shadow Torch not far into the game. You must first acquire the wall jump ability and have met Mappo, who will give you access to your map. In the same room as Mappo will be a Terminal. By using this terminal, you can unlock new skills or weapon moves in exchange for Money.
Upon finding a terminal, interact with it by pressing Square and select Unlock Skills. This will bring up a skill tree of branches paths, that you can select certain paths and learn those skills. More branches will open up when more weapons are acquired. Navigate the tree by using the analog stick and select skills to view by pressing X on them.
A new window will appear, with a skill description, along with a video of the skill being performed. Each skill costs a specific amount of money. At the top right of this screen, be a cost next to a coin symbol. If the number reads 100, you need 100 money to buy this skill—if you want that skill, press X again to purchase it or Circle to cancel and select a different skill or none at all.
If you look to the top-left of this screen, the amount of money you currently have will be displayed. If you do not have the required money, underneath the skill description in red will be a bit of text that says Not enough money.
Some Skills require Data Disks and no money. These disks are found when killing bosses and the like. But as you progress through the tree, some will require both.
Looking for more F.I.S.T. Forged in Shadow Torch guides? ProGameGuides has you covered!