To get gear naturally you can do the dungeon closest to your level and from quests of your level, including job quests. You can press Recommend Gear in the character window to automatically equip the best item level gear from your armory chest.

You can buy it from the NPC merchants but this gear is low quality compared to the high quality versions sold on the market board, but they are usually more expensive on the market board.

Below level 50, it's common to be over 10 item level below your level because of how the quests give you gear.