This achievement is earned by completing the main quest "Daughter of Giants" which appears once you reach level 10.
You shouldn't find this quest too difficult because it is designed around the level that you receive it at. In other words you wont be outmatched on level. There are a few stronger enemies whom are usually on their own, and as such can be quite simple if you use control.
General tip: using controlling abilities (e.g. stonefist for DK) makes the enemies easier to beat particularly if fighting groups, also do not be afraid to use your ultimate, they often come back quite quickly.
*** Spoiler - click to reveal ***You will travel back to Coldharbour to rescue Lyris, the giant woman that saved you at the beginning of the game.
You will mainly be fighting daedra as you complete four stages: face her regret, get her armour, get her weapon, and face her fear.