Skill Types
The game doesn’t have spells or ranged classes. You’ll be fighting using various melee weapons and learn skills by spending skill points the more you use those weapons. You can use any weapon of your choice. There are three Skill types in the game: Sword Skills, Battle Skills, and EX Skills. Sword Skills are your main attack skills while Battle Skills are your support skills (healing or buffs). Sword Skills are tied to the weapon is only available when you have that weapon equipped. That's why they have their own palettes. Whenever you equip a new weapon type, you have to set the command palette again.
Battle Skills from other weapons can be assigned to the palette of the weapon you're currently using. For non-active battle skills, it's better to put them in the main palette. As for active battle skills like Bull Rush, it's better to put them to your Command Palette instead. Each weapon has its own skill progression though there weapons where specific skills intersect, allowing you to learn those skills from either weapons. It’s recommended to try other weapons and use them enough to increase their proficiency to gain skill points and so that you can access and unlock other battle skills.
Skill Points
You earn Skill Points by reaching certain proficiency thresholds when using the weapon consistently. There are also rare occasions that defeated enemies give Skill points as well.
Skill Mastery
Consistently using a weapon increases its proficiency. There are certain skills that have proficiency requirements and require you to learn the preceding skill first before you can get it. In the screenshot below, I won't be able to unlock Horizontal Square (prof. req. 250) without learning Vorpal Strike first (prof. req. 150), even when my 1H sword proficiency is already at 288.
EX Skill
Extra Skills are special skill trees that encompass multiple sub skills. There are five EX Skill trees that you can unlock; however, you can set one Extra Skill at a time (Don't forget to set it after unlocking it in your Skill screen). The EX skills also require skill points so it will be efficient to focus on one EX skill tree that fits your Combat style. Like normal skills, there are skills in the EX skill tree that can be availed immediately as long as you have enough skill points and there are others that require skill level proficiency before you can purchase them. As long as you have the EX Skill tree equipped, you'll earn proficiency for it automatically.
Certain EX skills are also locked. To unlock them, you can press X to display their pre-requisites. So far, each EX skill tree has at least one locked skill.