There are certain things that you do in Valheim that will get you to experience with certain skills, such as when you chop down trees, attack with weapons, swim, sprint, and more.
The more you do an action, the more its level will increase and further improve how effective you are at performing such actions.
Using weapons will make you more proficient with them while performing different kinds of movement will make it easier for you to do them as the level progresses.
How to Level Up Skills?
There are many ways for you to level up skills depending on which skill you are focusing on but most of the skills only require one action to level them up, which you must repeat often.
For weapons, you can level their skill levels up per weapon based on which type you use, which for example would be the Sword skill gains experience when you use sword-type weapons or your Knives skill increases if you use knife-type weapons.
Movement skills are simple and will level up based on how much you perform different kinds of movement such as your Sneak skill increasing when you sneak around or your Jump skill increases if you always jump.
Valheim Experience System
Leveling up in Valheim mostly focuses on you increasing the skill levels that you have by doing actions that involve them.
Whenever you use up stamina to do an action, this causes the skill to gain experience and eventually level up based on how often you do the actions.
The more you do an action, the faster it will level up and this allows you to gain a good number of levels by repeating the actions when you have a lot of stamina.