As you travel through the land and accomplish the heroic tasks set before you, your character will earn experience points and gain character levels. With each level comes an increase in maximum Health (which makes you harder to kill) and an increase in Energy (from which you draw power for many skills). The highest level your roleplaying character can reach is 20, which is, not coincidentally, the starting level for a ready-made PvP character.
Each level awards you attribute points to spend improving your attributes. Your primary profession determines your primary attribute, such as the Elementalist primary's Energy Storage, which permanently increases maximum Energy, allowing you to use more skills more often. The number of points you receive when you gain a new level increases as you gain more experience.
With experience you'll gain skill points, which entitle you to train new skills from your primary and secondary professions. With each skill you learn, your skill arsenal becomes more versatile and overall more powerful in a wider range of situations against enemies of various types.
Quest-giving NPCs (non-player characters—the computer-controlled people that inhabit the game) can also sometimes be seen as de facto skill trainers, since a new skill (or set of skills) is often included in the quest's rewards. In this way you can learn plenty of extra skills without spending a single skill point, and you will likely unlock most skills earlier in the game in this fashion. Skill points are valuable and rare—you will earn one for every level you gain, and from certain important quests and missions, but you should not spend them frivolously. If you see an NPC offering a skill as a quest reward, and the same skill is for sale from a trainer, you're better off hitting the quest.
You can create six very different characters for your Guild Wars account, each taking advantage of a unique set of resources including skills, attributes, weapons, fighting styles, and strategies. Your Warrior/Elementalist can hit the enemy hard with distance spells, and then rush into combat where you'll then knock them down with a hammer blow. A Ranger/Necromancer can use both beasts and the reanimated dead to pummel foes while battering enemies with ranged arrow attacks.
The professions, skills and attributes you choose to learn and improve over time result in a unique Guild Wars experience for each hero you create. You can further customize your hero by choosing the character's sex, appearance, and make your armor set unique with dyes that you might find as loot or purchase from a dye trader. And don't forget, you can delete a character at any time to free up space for a new one.