Minecraft world seeds are generated by entering a string of characters (including negative or positive integers) into the "World seed" box within the Minecraft menu. As few as one character can be used, and each number will generate a unique world. Text strings are converted by the game into numbers.
The in-game algorithm allows the generation of the same world every time if the same value is input into the seed generator for example the old village that if you spawned in before the village and pillage update will be gone after the update. However, when the algorithm is updated and changed, it no longer generates the same world it did in the past. In other words, seeds that worked for older versions of Minecraft may not work for newer versions and different editions like java and bedrock won’t be the same. Because the world is only generated up to 10 chunks away from where a player has been, chunks further away than this will be generated according to the new algorithm. This creates sudden terrain changes and cliffs if the algorithm changed dramatically, and more minor terrain inconsistencies if the change was less drastic. These variations can create buildings with missing parts, and can even result in easy access to treasure rooms in Ocean Monuments. Also, it's important to keep in mind that seeds for one version of Minecraft, such as Pocket Edition, may not have the desired result in another version, such as Java Edition.
In Java Edition, the player can use the command
/seed to view the world's seed.
In Bedrock Edition, the seed can be found on the "World Options" screen.
There are many possible Minecraft world seeds, although only a few will generate unique, interesting terrains and structures.
Bedrock Edition seed picker
In Bedrock Edition, the seed picker interface allows the player to choose from a number of preset seeds for generating worlds with specific interesting features near the spawn point. This interface can be accessed via the arrow button next to the "Seed" input field when creating a new world. The seed picker interface shows a search box and a scrollable region of named thumbnails to browse the preset seeds. As of Bedrock Edition 1.13.0, there are eighteen preset seeds.
A list of blog posts that provide examples of world seeds can be found here.