Divine Orb is one of the most expensive and rarest Orbs in Path of Exile. Divine Orbs have an average exchange ratio of around 1 to 35 to Chaos Orbs, and 5 of them can be traded for one Exalted Orb. For most players, they have very limited uses, as they should be only used to min-max items that are worth couple of Exalted Orbs or more to make it worthwhile. Divine Orbs are used to modify numeric values of Explicit modifiers on an item. It basically means that you need an item, that you are willing to spend a couple of Divine Orbs to increase it's stats just by a couple of percents, in the best case scenario maybe 10-15%. Not to mention, like with most other Orb types, using Divine Orbs doesn't guarantee instant success.
Divine Orbs can be found anywhere in the game, looted from slain monsters, dropped from chests, destructible objects and strongboxes. They have a slightly higher drop chance from Arcanist's Strongboxes and Blighted/Legion Chests which are guaranteed to drop Currency items. Obviously the higher the Monster level, the higher the chance to drop Divine Orbs and other higher Tier Currency, but the chances are still extremely, whereas you can complete tons of Maps and find not a single Divine Orb in them. If you are a casual player and you come across a Divine Orb on your journey, you should primarily consider exchanging it for Chaoses or Exs, and buying a gear upgrade. 1 Divine Orb will usually suffice to purchase one or two solid Rares that will work in Mid and Higher Tier Maps. Divine Orbs also have an interesting property that's not directly indicated in its description. When new Patches introduce significant changes to Unique Items, sometimes you may be able to change the outdated Items stats to the new current version of the Item. However, it's not always recommended, as on many occasions the older version will have significantly better stats. For example, using Divine Orb on Legacy Kaom's Heart (with 1,000 bonus Maximum Life) would lower the Life bonus by half (and you would be basically throwing away a couple of Mirrors in the process).
Divine Orbs are used by high-level players in the process of meta-crafting to min-max the stats of end-game gear. Since their drop chance is so low, most likely no one would be able to provide themselves with enough Divine Orbs to complete their items, and obtaining them via trading is usually the only efficient way. Like all other Orbs, you can buy them using real cash on the Odealo marketplace. You can go to Odealo to buy PoE Divine Orb at the best possible prices and in any quantity. With multiple sellers offering Divine Orbs for sale, you can buy them all the platforms available including PC, Xbox One, and PS4, and on all available Leagues and game modes including Standard, Softcore/Hardcore, and permanent Leagues like Blight and Metamorph.