Valarjar is a new faction introduced in Legion, and is mostly tied to the Stormheim zone. Doing all the quests in this area will get you to 0/12 000 Honored, and most of the quests in this zone awards reputation. If you want to go for exalted, the first step should be to complete every quest you come across in Stormheim.
Once you've done all quests, getting rep is a little bit harder, but there are several ways to gain it:
1) Complete World Quests in Stormheim. These will pop up on the map when they are available at level 110. If you are unsure which faction the World Quest is tied to, mouse over it, and it will tell you. Also make sure to do any Warden quest in Stormheim, since these gives rep with both The Wardens and Valarjar.
2) The two dungeons Maw of Souls and Halls of Valor awards 250 rep each from killing the endboss.
3) Do Kirin Tor Emissary Quests. Once you do 4 of these, you can pick a reward, including an item that gives you 1 500 reputation with Valarjar.
4) Do regular Kirin Tor quests. These awards rep with the faction in which zone the quest is located, so do all that are in Stormheim.
5) Loot Treasure Chests. The treasure chests in all Broken Isle zones can drop Insignias which gives +250 rep for a faction, and can include the insignia for Valarjar. The insignias has a really low drop chance, but you will get a few if you pick up all the treasure chests available.
6) Order Hall missions will also occasionally include quests which gives insignias that awards reputation, so make sure you complete these.
Once you have the desired reputation, you can find the quartermaster in Valdemar in Stormheim.