To save your 3D model in Blender as an OBJ file, follow these steps:

1. In the top menu, go to 'File' and select 'Export'.

2. Choose 'Wavefront (.obj)' from the list of available file formats.

3. You can adjust the export settings such as scale and smoothing options in the left-hand panel before exporting.

4. Click 'Export OBJ' to choose the file location and save your model as an OBJ file.

Exporting your 3D models as OBJ files allows you to use them in various other 3D applications and game engines. This file format is widely supported and can retain important information such as vertex positions, normals, UVs, and materials.

It's important to note that when exporting as an OBJ file, Blender will create a separate .mtl file that contains material information. Make sure to keep the .obj and .mtl file together in the same directory when using them in other applications.

By following these simple steps, you can easily save your 3D models in Blender as OBJ files and seamlessly integrate them into your 3D projects. Happy modeling!