Basically, you punch and kick this type of bag/makiwara slowly and repeatedly in order to condition the striking area as preparation of hitting a opponent full power. It is especially used for conditioning the shin to be used as a effective weapon (and prepare it for those godawful shin vs shin collisions of shin lowkicks vs shin-blocks).
It is not used to perfect formal technique (getting hip movement and so on right) as a regular maikiwara, or to practice combination&power as a regular bag.
But Im certainly not an expert in using this, and should not try to guide anyone in its use.
Martin Hultgren
Kyokushinkai, Sweden