If you've created a 3D model in Blender and want to share it with others or use it in another program, you'll need to save it as an OBJ file. Here's how to do it:

1. Open your 3D model in Blender.

2. Go to 'File' > 'Export' > 'Wavefront (.obj)'.

3. In the export settings, you can choose the location to save the file, set options such as scale and smooth groups, and then click 'Export OBJ'.

And that's it! Your 3D model is now saved as an OBJ file and ready to be used in other programs or shared with others.

Keep in mind that while OBJ files are widely supported for 3D models, they may not preserve all the details and materials of your original Blender project. For more complex models with textures and materials, you may need to explore other export options or file formats.

In summary, saving an OBJ file from Blender is a straightforward process that allows you to share your 3D model with others and use it in various applications. It's a crucial step in the 3D modeling and 3D printing workflow, and knowing how to do it will make your work more accessible and versatile. Happy modeling and exporting!