Whenever you create a new world in Minecraft it will be assigned a random unique value called a 'seed' which will allow you to share it with other Minecraft players. Any changes you make to the world after will not show in the newly created seed. You will not spawn in the same location on the seeds you create but in random places on that world. If there is a major update to Minecraft you may find thay your seed will change in some way from the previous version.