First of all, placing of the constructor block is slightly different. You need to place it at the center of the area you want to change rather than the front left of where you'd want the building to appear.
Once it's placed, hire a terraformer and choose 'terraform area'. You'll then see the screen shown to the right. These are the current options to choose from, click one and it will start right away. Before you do, you should check the radius at the bottom, this by default is set to 30, which means the affected area will be from the constructor box to 30 blocks to the North, east, south and west of it. A radius of 500 would affect 1 square kilometer.
At least one chest will be needed in the area of the constructor box to supply the terraformer with dirt, saplings or whatever they need to terraform the land. They will let you know what they need using the caption above their heads. Terraforming can take a long time and use a lot of dirt, so be sure you have plenty.
Here is a description of each option along with details of how it will affect the land. First of all, none of these options will change the biome, only the look of the land/sea.
|NAME||Constructor box position||Requires||Effects|
|Sealand||Above the water level||Dirt||Converts all water (sea and rivers) into dirt from the top level right down to the sea bed|
|Nature||Place at highest point you want to affect. Eg on top of a hill||Saplings, one type or a mixture||Randomly place saplings, you can fire the worker when they've reached the desired density.|
|Lawnmower||Place at the highest point (like Nature option)||Empty chest only||Cuts all tall grass on the level of the constructor box and below it, so place on top of hill.|
|Flattenizer||On the level you want to flatten to.||Empty chest to collect dirt||Removes all dirt, grass and cobblestone to flatten area, will not remove ores|
|Value Pack||On the level you want to have flat land.||Dirt||Cheap version of Sealand, this will only place ONE layer of dirt to form flat land and can be use on sea or land.|
|Glacial||On highest point you want to effect||Buckets of water||Turns water into ice and drops snow onto the land, even in the desert.|