How to build a world

first you have to go the tittle page and click on create a new world

Then you can click on creative or survival then click on create world.

Tips for your game

first you can go into cheats and make it always day and no rain with wether cycle

the other thing is command blocks. What you have to do is in chat type /give @s command_block. Once you do that you can obtain the command.

another tip is barrier blocks. It can only be seen by holding the block and in command is /give @s barrier.