The Undaunted line is progressed by earning Reputation rather than using the skills in the line. Reputation is gained by completing the in-game achievements under the "Group Dungeons", "Veteran Dungeons" and "Trials" sections of the Dungeons achievement category. This basically involves going through all the dungeons, killing all the bosses, and completing all the optional challenges. After you hit Level 45, you can also gain Reputation by completing Pledges. See UESP: Undaunted Reputation for more details.

The Assault (and Support) skill lines are progressed by levelling up your Alliance Rank, which in turn is achieved by gaining Alliance Points in Cyrodiil. See UESP: Alliance Points for more details.