dBodyAddForceAtRelPos

My editor has a physics tool that lets you click on the screen, and push or pull the object around. Right now, it just adds a vector to the whole object. I want it to add force and torque, so that if I push the edge of it, the box spins, but if I push the center, it goes straight. Will this command add force and torque based on relative position and the dimensions of the rigid body?

Yes.

dBodyAddForceAtPos() adds a force at a given position relative to the world.

dBodyAddForceAtRelPos() adds a force at a given position relative to the body's center of mass.