Rigging an OBJ for 3D modeling and animation involves creating a skeleton or structure to control the movement and deformation of the 3D model. Here are the basic steps to rig an OBJ:

1. Import the OBJ: Start by importing the OBJ model into your 3D modeling software. This can usually be done by selecting 'import' and browsing for the OBJ file on your computer.

2. Create the skeleton: Once the OBJ model is imported, you will need to create a skeleton or joint structure to define the movement of the model. This is often done by using a tool such as a joint or bone tool to place the skeleton within the model.

3. Bind the model to the skeleton: After the skeleton is created, you need to bind the model to the skeleton. This involves assigning each part of the model to a specific joint or bone in the skeleton. This allows the movement of the skeleton to deform the model.

4. Set up controls: To make the rigging process easier for animation, it's important to set up controls for the rig. This can involve creating controllers or handles that animators can use to pose the model more easily.

5. Test the rig: Once the rig is set up, it's important to test it to ensure that it deforms the model properly and allows for the desired movement. This may involve posing the model in various ways to see how the rig behaves.

6. Refine the rig: After testing, you may need to refine the rig to fix any issues that arise. This can involve adjusting the weighting of the model to the skeleton, adding more controls, or making other adjustments to improve the rig.

7. Finalize the rig: Once the rig is working as desired, it can be finalized for use in animation. This may involve cleaning up the rig, organizing controls, and preparing it for animation.

Rigging an OBJ can be a complex process, but it is essential for creating realistic and dynamic movement in 3D models. By following these basic steps, you can learn the fundamentals of rigging an OBJ and begin creating your own character rigs for animation.