Implants are special items that grant you bonuses to your skills.
There are no set maximums on your skills so these do not increase that, nor do they take up any IP, they quite simply add a few points to what you have already bought.
For example: say you have 31 points in Energy Weapons, and you equip the Waist Implant (Level 1), which has +8 Energy Weapon Skill, your skill will raise by 8 points to 39.
Implants require captain level, and an available (relevant) slot.