Force Points (フォルス・ポイント?) or FP for short are essentially the currency of the game. In Hexyz Force, there are no shops to buy/sell items, but you will eventually gain access to a Fusion menu, where items can be synthesized by costing FP. You earn FP from battle and breaking down items.
Other than Fusing items, FP is used to raise levels of Tech, Atk, and Reso on your Ragna- facts. The amount increases as the levels rise. FP is also used to create new pathways on the field and is what the Restore function runs off of (it costs 10x your primary character's current level).
Another use for Harvest Points is the orbs in the Tower of Judgement. Force scan them to activate to be used up to 10 times, but the prices vary on each floor.