The way in which Bilbo acquired the ring is rather peculiar and important too. The whole plot of the Lord of the rings is based on this event.
…….After the dwarves , Bilbo and Gandalf left Elrond’s house, they started their journey of deceptions and dead ends. They travelled on these paths for a few days and on one such day,they required rest. They found a comfortable cave and after thorough inspection, decided to take a short rest. This was perhaps the biggest mistake made by the company but this is the event due to which the ring was found.
As they slept in the cave, Bilbo noticed a crack developing at the back of the cave. Alas, it was too late. Before they knew it, they were in the custody of the goblins and were chained.The company was insulted and suddenly the lights went out. The Great Goblin fell,dead. Gandalf had come, of course.He firmly asked them to follow him. They were safe, for now……. Little did they know the Goblins were at close quarters. They stealthily caught up with the company and they were all caught again. All, except Bilbo. He bumped his head on a rock and remembered nothing more.He soon got up and started looking around. He knew the Goblins weren’t close, yet they were not far away. As he explored the cave , which seemed to have no end, he found a thing made up of cold metal, the Ring. He walked into some water. It was a pool of water and Bilbo decided not to wade in it for he thought of slimy creatures in it.Deep down in the dark water, lived Gollum.He had two round and enormous eyes and had a thin face. He had spotted Bilbo and was looking intently at him. He did meet him and the two of them had a round of riddles . If Bilbo won, Gollum promised to show him the way out and if Gollum did, he would eat Bilbo.
Gollum asked him:
This thing all things devours.
Birds, beasts , trees ,flowers
Gnaws iron, bites steel,
Grinds hard stones to meal,
Slays kings, ruins town
And beats high mountains down.
The answer, of course, was time
He then asked him , “What do I have in my pocket??” It was the ring of course.