I don’t know what are you trying to do so I will just explain collsion from what I know.
So basicaly there is two types of collision Simple and Complex.
Simple - Made of convex. Automatic generation is ok for small meshes for bigger with important collsion use custom collsion instead.
Complex - Better as it use mesh as collision. But can’t be used for physics simulation…
And you can always create custom collsion in blender and import it with mesh.
Read more:
There is also site on wiki about blender. You might want to take a look at it.