To be able to use Chipset, you need to meet some certain conditions. For example:
The conditions are your digimon's minimum level is 25 and must be Nature Spirits. This Chipset will increase your digimon attack by 21 points. Chipset lv means your digimon need to reach at least that level to be able to use it, and digimon lv indicates your current digimon's level. After you reach all the conditions, it will show you "Able to apply ChipSet Ability" instead of "Unable to apply ChipSet Ability.
See the picture which appointed by the arrow, you have 2 available slots. You can insert your ChipSet in your digivice by drag your chipset into available slot. Remember, once you inserted it, the ChipSet can't be sold to another tamer. It will become your personal item.