Implants are hardware that you can plug into your character's brain to boost skills and attributes. They are somewhat hard to find.
Train up your Cybernetics skill to at least level 1, then right-click on an implant that you have the requisite skills for (check the information window), and choose to install the implant. It will be in effect immediately. If you remove the implant, it is destroyed. You are not harmed, though.
You can have up to ten implants installed at a time, if you have Cybernetics trained to level 5.
One type of implant is a skill hardwiring implant. This type can be plugged in to increase the skill specified in the implant's description.
Another type of implant is the attribute-boosting implant. This type will increase the number of points of the attribute specified in the implant's description. The increase ranges from 1 through 5, depending on the implant.
If you get podkilled, your implants are destroyed. If you have jump clones, each jump clone has its own set of implants. If you jump from a clone that has implants, you will not be able to use the implants in that clone until you jump back to it.