Nexus War is a browser-based, multi-player online game. You, as a player, explore the game world and interact with other players through your characters. You are allowed three characters for free, but may donate and obtain additional character slots.
Each character has a limited number of Action Points available per day. You use Action Points to do things, generally to gain Experience Points through actions like combat, crafting, or book reading. Nearly every thing your character does will consume 1 or more Action Points (usually 1). Characters "regenerate" 1 Action Point every 15 minutes.
Each character has a number of Hit Points and Magic Points as well. If you character takes damage (such as from combat), you will lose Hit Points. If your Hit Point score reaches zero, you will die.
The most important thing to know is that death in this game is not permanent. If your character is killed, you may simply "respawn" and poof: you're back in the game. Respawning costs Action Points (1 per level) - and at the early stages of your character's existence, this is pretty minor.
As your characters interact with the world, they will gain Experience Points. Various actions will gain you experience (such as combat, or reading books, repairing buildings, or even picking locks). When you accumulate enough Experience Points (or XP) you will gain a level - and with it, additional Character Points.
You use Character Points to purchase new skills, which advance your character's power. These skills either allow you to do new things like Fly or Cast Spells, or they improve the capabilities you already have, like Search.
At levels 10 and 20 you can choose a new Class. Different classes have different skills. A character can gain a maximum of 30 levels, and many have.
Another important thing to know is that your choices are permanent. Once you choose a character class or skill, that purchase cannot be undone - so be sure.
You may restart any character from scratch. You may delete the character and start a new one, but you may not change the skills on an existing character. Restarted characters have no special in-game advantages (like extra skills). Any equipment obtained will be lost if the character is deleted.