Each time your commander levels up he/she gains skill points that you allocate at your discretion. Once you use a point for a skill it remains there until you use a skill reset. A very useful strategy in Mobile Strike is to allocate your skills depending on what you are doing. If you are peacefully developing your base, upgrading buildings and researching, then there is no need to waste skill points on attack skills. The left side of the skill tree is for your military might while the right side is for your economy. Use skill resets to switch your skills back and forth as you need, it makes a huge difference. A skill reset is 1,000 gold in the store and is well worth it. A better solution though is to have your Alliance higher-ups put skill resets in the alliance store so you can use your loyalty funds to purchase them.
What does Commander Skill Reset do in Mobile Strike?