To elaborate: Essence isn’t removed from your account as you purchase abilities, since the total amount of Essence you have earned contributes to your character account’s level. For example, this account is Level 3 since I’ve earned 10,714E in total from writing/events. This has a lot to do with Level Progression, which is covered on the
Character Growth and Currency page of the rules.
When you purchase new abilities (which must be approved via the
Purchase An Ability form), you can keep track of these purchases using a simple purchase log.
Here’s an example of a purchase log from my profile.
In addition to keeping track of your purchases, though, you also gotta keep track of your Total Spent Essence. This is so you don’t accidentally go over your Earned Essence counter/spend points you just don’t have. I just keep a “Total Spent Essence” marker at the top of my profile as a reminder for myself, which I update every time I add a new ability to my character’s profile.