1. Download any codebase
2. Open up Dream Maker. Can be opened with CTRL+M or by clicking the gear in the top right corner of the byond hub screen.
3. Click File in the top then click Open Enviroment. Open the enviroment in the codebase file you downloaded. Should have a cube icon.
4. After opening the enviroment file, click New in the File menu.
5. Click the dropdown box. Click .dmm file.
6. Happy mapping, I believe.