Category cables use RJ45 connectors and are backward compatible with lower tiers. Here is a breakdown of some of the differences, and why would choose one category over another.
Cat5e cable is the minimum standard used for LAN drops. It has a bandwidth of 100 MHz. It is used in 100Base-T Ethernet. Its maximum data rate is 1 Gbps at up to 100 meters, when introduced it was a large upgrade over the 100 Mbps rate of Cat5.
Cat6 Rating requires more stringent specs for cross talk and system noise than Cat5e, Cat6 cable is able to support gigabit Ethernet. It is also used for phone lines and in residences. It has a bandwidth of 250 MHz, and its data rate is 1 Gbps at up to 100 meters and 10 Gbps at up to 37 meters.
Cat6a is routinely used for gigabit Ethernet in data centers and commercial buildings. Its 500 MHz bandwidth is double that of Cat6 and its data rate is 10 Gbps up to 100 meters. Cat6a is commonly shielded twisted pair cabling, which makes the cable heavier, more difficult to bend and up to 30% more expensive.
Cat7 cable has the same data rate and distance specifications of Cat6a (10 Gbps up to 100 meters) however it offers 100 MHz more bandwidth and costs about 20% more. It is used for 10 Gbps critical infrastructure and is largely found in data centers. Its performance is similar to Cat6a but it has more shielding.
Cat8 was designed only for data centers where distances between switches and servers are short. You can use cat 8 cables in standard office applications, however that is not what they were designed for. It is not intended for general office cabling. Cat 8 supports up to 2000 MHz, 25Gbps but only for distances up to 30 Meters. It is typically thicker shielding than Cat 7
568A and 568B are the wiring standards that define the order in which colored conductors are terminated.(Color Code). 568b is the industry standard for patch cables. Its important to note, the pin-out for both 568a and 568b is the same, straight through. The only difference between the two standards is the placement of cable pairs on set pins, functionally both standards are the same.