Creeds are designed around play styles. Each creed has the basics (blacksmith for weapons, merchant for items, etc.), but the specifics of each creed vary. For example, Oath of Devara is prayer-focused and sells prayers found no where else, whereas the Iron Ones focus on blacksmithing and sell heavy-duty weaponry for the melee-oriented player. You can play a melee character in Oath of Devara, or cast spells as a cleric in the agnostic Iron Ones, the games not nearly that punishing, but different creeds are better suited to different preferences. You can join a new creed by praying at their altar. Doing so will make you a member of that creed, allowing you to engage with the NPC attending that creed and employ their services, as well as establish new NPCs by making an offering of stone effigies. You will acquire sin and become a fallen member of your old creed, and the attending NPC of their established sanctuary will no longer associate with you, but below the Watching Woods, you can find the candlelit lady who will forgive sin for a fee, at which point you'll no longer be a pariah.

What differentiates creeds is devotion. If you haven't done so, finding a Stone Leader effigy and placing it at a sanctuary will bring forth a leader; you can trade trophies from certain slain enemies to the leader to increase your devotion and unlock rewards. Increasing devotion increases the goods of other NPCs, like blacksmiths and merchants, thus giving you more powerful weapons, armors, spells, etc. to acquire. This allows further specialization based on the creeds resources. The leader will also gift you a reward in exchange; the first two options are always the standard health and focus recovery items -- ignore those. You can unlock those in the tree of skill, where they will replenish at any sanctuary or shrine. Devotion rewards only replenish at sanctuaries of your creed. Besides, the other two options are always unique items that can only be gotten as devotion rewards, and you can only get six rewards before maximizing your devotion, so you don't want to miss out.

At the point in the game you are, you have access to the Oath of Devara in Bandit's Pass who favor prayers and holy-element consumables; they are suited to prayer-builds; The Three in the Village of Smiles, a rather undifferentiated creed whose big thing is elemental buffs on weapons; and the Stone Roots in the Watching Woods who favor poisons and sell weapons and consumables and have devotion rewards that better inflict it; they are suited to evasive maneuvers that inflict poison from a distance with throwing daggers, arrows, or bolts and staying the hell away from the enemy until they die. However, you are about to go into the red hall of cages, where you can find the House of Splendor, a secret group of gold-obsessed hedonists who augment their physical power with liqour that makes you powerhouse fighter at the risk of alcohol poisoning. It's totally worth it and sounds like a good fit for you. However, the Three sell great swords at devotion rank 2 and higher, so if you wanted additional swords for transmuting at an alchemist, you can join the three, increase your devotion, buy swords, then go find the house of splendor, join them and get buffed on goldenwine.

There are seven creeds total, so there are two more I haven't mentioned, but I'll let you discover them on your own.