How exactly do you get an essence yourself and not buying it or trading for one from another player?

Besides buying from the trade broker or diamond shop, you can find them from mission satchels, battling, dungeon boss chest or nurturing. These drops are very rare though, which is probably why essences are expensive. They can also drop from Jinxie Jamboree if you get to the bonus game I think.

Some festivals also have games where essences are given out as prizes.

Note that only regular and enhanced essences can be found. Mystical essence can only be bought from the diamond shop, or if someone is selling them.

Ok then that was really helpful. :)