There are a few tools you will need to get used to.
- The default tool is "Select," and it is self-explanatory. It lets you select blocks within a cubic area to modify.
- The second tool is "move." You can move selected blocks with this.
- The third
& Knuckles lolis Clone. You can make infinite copies of selected blocks with this.
- The brush tool lets you draw or replace blocks with a specified shape and size. By default, it is set to cube, filled, and 1x1x1. The default block, however, is Stone (minecraft:stone).
- Our next tool would be Flood Fill or Bucket, which lets you fill in an area with a specified block.
- I totally do not know what "Generate" does. It has some options, though, like what you want, if you want a live preview, block preview, or GL preview. It also has iterations (Max 3 Min 1), and that's all.
- "Inspect Chunk" lets you inspect a 16X16X256 "chunk" of blocks.
- Inspect Block and Inspect Entity are similar, but on one target instead.
On the top, you will see options like "Camera View," which lets you view the world from a different perspective, "Time of Day," "Brightness," "Work Plane," "View Distance," and "Controls."
On the very top, you can see MCEdit, which opens or saves the world, Edit, which edits said world, Select, same as its tool variant except more limited, Import/Export for Schematics, Chunk, Plugins (yes, these can be customized), Window, Options, Help, and Debug. I won't go into detail of all of these, just Import/Export. That option lets you save or summon schematics. To save one, select blocks and click "Export Schematic." To load, click "Import Schematic." My favorite tool for the importing would be the Exports Window.
Right below those, you can find out how to use texture packs and versions with your world. But remember the fact that MCEdit WILL NOT work with mods.