Ascension refers to a late part of the game in which you need to complete in
order to progress through the game and storyline (Unless you get ran).

There are four trials to Ascending. You need to complete three missions -
Dunes of Despair, Elona Reach, and Thirsty River. Once you have completed the
three missions, you will then need to kill your Doppleganger, in which more
info can be found in the term below. Once you have done this, you will be
completely ascended and can progress through the storyline normally. Ascension
is technically not easy, but with practice, it becomes easier to do and
understand.

EXAMPLE: I still need to complete Thirsty River for Ascension.