Hi Gdar- welscome to Taborea. There are numerous "currencies" that can be earned in RoM. If you are doing dailies(and you should) then you are already familiar with Phirius Tokens and game gold.
The black codex vendors are "Collectors of Ancient Mementos". You gain Ancient mementos, or 'mems' as a drop from bosses in the instance runs. The lowest level run to have mems in Origin. IT is level 50 or 52, and you get there through Jade Valley in the northwest corner of the Aslan map. Heart of the Ocean is east of Boulderwind Village. It requires a set of attunement quests to enter. You want to get in on instance runs with friends and guildies. You don't have to reach the level of the instance to enter it, but the ones that have attunements will require you to finish those quests. Everyone in the party gets to loot the boss for however many mems it drops.
There are more Codex vendors you can reach outside Hall of Survivors, and then every zone after that has vendors with higher and higher levels of gear as you progress. Most players prefer boss gear to codex gear, but there is certainly nothing wrong with the codex stuff. Some codex gear seems to be oriented to specific class combos. For example they sell axes with healing bonuses. That's useful if you are a priest/warrior or druid/warrior, but pretty much no one else.
Enjoy the game. We need fresh prey..I mean.. new players. OMG- I can't believe I typed that out loud.