A keystone jack is the modular component where an Ethernet cable is terminated. It fits into a wall outlet or patch panel and forms the point where a device joins the network in the work area. Being modular, it lets different port types (RJ-45, fiber, audio) share one outlet frame.
Termination uses one of two methods. In 110 IDC jacks the conductor is pressed into the contact blade with a punch down tool; the blade cuts the insulation to reach the copper and trims the excess in the same motion. In toolless jacks the conductors are pressed by a closing mechanism, needing no tool and speeding field installation.
The most critical detail is the untwist distance. Each pair is twisted at a set rate to suppress interference, and the further it is opened at the termination the worse the NEXT value becomes. The standard limits this to 13 mm, so the jacket should be stripped as close to the termination as possible.
T568A and T568B are two colour schemes defining conductor order. They are electrically equivalent; what matters is using a single scheme throughout a project. Terminating one end T568A and the other T568B creates a crossover link, which causes problems outside modern auto-sensing equipment. T568B is common in installations in Turkey.
For RJ-45 plugs, cable type decides: plugs with different contact geometry are made for solid and stranded conductors. Using the wrong plug leads to contact loss over time. Screened (FTP) cables use metal-bodied plugs that carry screen continuity through the plug. Field termination plugs assemble without tools and are practical for end devices such as cameras and access points.