Murmuring Obols are a currency in Diablo 4 which can be spent at the Purveyor of Curiosities, a vendor found in towns in Sanctuary. If you're familiar with Diablo 3, this system is very similar to Kadala and the Blood Shards that you'd spend to buy a random piece of gear with the chance of it turning into a legendary item or set piece.
This means that Murmuring Obols are important for getting certain legendary aspects aside from completing Diablo 4 dungeons. Oh, and you can buy whispering keys with obols as well, which allow you to unlock randomly spawned silent chests in the overworld. With that in mind, here's how to get Murmuring Obols in the Diablo 4.
How to get Murmuring Obols in Diablo 4
Early in the game, the most consistent way of earning Murmuring Obols is from random overworld events. These can spawn all over the map and can be completed solo, though they are much easier with a group. Each event has an optional Mastery requirement, and you'll net extra Obols if you complete it, meaning you can get a maximum of 35 Murmuring Obols for each event. You'll also be randomly rewarded with Murmuring Caches, a consumable item that gives you 50 Murmuring Obols when used.
This currency doesn't go into your bags, so don't bother looking for it there. Instead, you need to open your character sheet (press C or I) and click the "Materials and Stats" button to the right of your character window. A narrow window will pop out and here you can see your currency. You'll notice a cap on how many Murmuring Obols you can hold, though you'll likely be able to increase this later in the game. In the meantime, make sure you spend those Obols if you're close to the cap so you don't lose any.
Diablo 4 Murmuring Obols: what to buy with this currency
You can find the Purveyor of Curiosities in many of the towns in Sanctuary, and you'll see that they sell random pieces of gear and a mysterious Whispering Key item. The only thing you choose about the gear you buy is the slot it can be equipped in—the rest is left to chance.
If the Purveyor of Curiosities follows the same mechanics as Kadala from Diablo 3, there's a 10% chance that the item you buy will be of legendary quality. As the currency to buy them has a cap, you're not losing anything by taking the risk, especially as you can salvage any gear you don't want for crafting resources.