Essence orbs are used to create and define your avatar. There are three major orbs. Orb of Dreams defines your mind, Orb of Manifestation defines your body, and Orb of Ascension defines your spirit. You will need all three orbs to complete your avatar so it can travel through the maze.
As you collect better memories, you will be able to create more powerful orbs. You can replace weak orbs with more powerful orbs to improve your avatar. While memories and orbs have levels as a convenience for tracking relative power levels, your avatar does not gain XP or levels, nor does it need them. Your avatars attributes, skills, and abilities are solely defined by it's current orbs. There are absolutely no prerequisites to use any orb.
There are minor sparkling orbs that can add bonuses to your attributes or skills. You can have up to seven of these minor orbs to supplement your three main orbs. You can see a total of ten orbs on the avatar in the picture below. The seven golden orbs arranged in a halo around the avatar's head are the sparkling orbs. The large three orbs from top to bottom are Orb of Dreams, Orb of Manifestation, and Orb of Ascension.
Note the two sample orbs that were created from the same three cards. While their attributes and skills are fairly similar, you can see that they differ greatly in their numeric values due to random generation. You will want to create many orbs in your search to improve your avatar.