Blender is a popular open-source 3D modeling and rendering software that supports various file formats, including OBJ, which is commonly used for 3D models. If you want to open an OBJ file in Blender, follow these simple steps:

1. Launch Blender: Open the Blender software on your computer. If you don't have Blender installed, you can download it for free from the official website.

2. Select 'File' > 'Import' > 'Wavefront (.obj)': Once you have Blender open, go to the 'File' menu at the top-left corner of the interface. From the drop-down menu, select 'Import' and then choose 'Wavefront (.obj)'. This will open a file browser window.

3. Locate and Select Your OBJ File: In the file browser window, navigate to the location where your OBJ file is saved on your computer. Select the OBJ file and click 'Import OBJ' to load it into Blender.

4. Adjust Import Settings (Optional): Depending on the complexity of the OBJ file and your specific project requirements, you may need to adjust the import settings. Blender provides options for scale, rotation, smoothing, and other parameters to ensure the imported OBJ file looks as expected.

5. Work with the Imported OBJ: Once the OBJ file is imported into Blender, you can start working with it in the 3D viewport. You can manipulate, texture, animate, and render the 3D model as per your design needs.

6. Save and Export: After making any necessary modifications to the imported OBJ file, you can save your work in Blender's native file format (.blend) or export it to a different file format for use in other 3D applications.

By following these steps, you can easily open OBJ files in Blender and integrate them into your 3D modeling and rendering projects. Blender's intuitive interface and powerful features make it a versatile tool for working with 3D models in various formats.