Sorry if this goes on a bit but you seem to be looking for a technical primer, so just as a bit of expansion:
While an inadequate/faulty cable can limit the speed, the cable does not determine the speed of the connection. That’s determined by the capabilities of the network interface card (or NIC) in the devices at either end.
Most NICs today are capable of 1 Gb/s, so you need a cable capable of supporting this speed. Very old equipment may have NICs that are only capable of 100 Mb/s. (And equipment with 2.5 Gb/s NICs is just starting to appear on the market).
When first connected the two devices will negotiate the best speed both can handle to avoid too many errors. Sometimes this negotiation screws up and they will use 100 Mb/s instead of 1 Gb/s. (Simply disconnecting and reconnecting should fix this).
The cable you need is known today as “Ethernet cable”. (This is actually a misnomer, its real name is unshielded Twisted Pair cable or UTP. Ethernet is a transmission standard, not a cable). The main standards are:
Cat 5….obsolete, only capable of 100 Mb/s…don’t buy, (even if you can still get it, which I doubt).
Cat 5e…Cat 5 “enhanced”. This is capable of up to 1 Gb/s and will do the job.
Cat 6…a redesign specifically for 1 Gb/s. Unofficially capable of 10 Gb/s at up to 55m. Probably the most appropriate for home use today.
Cat 7...will work but it was really designed for 10 Gb/s connections and over the top for home use.
Cat 8...will also work but it was designed for very high-speed connections in data centers, as an alternative to fibre optic. Way over the top for home use.
The standard specifies that the cable should work up to 100m. (Working techs tend to keep it to under 85m). Note, all eight wires have to be connected for 1 Gb/s. If one wire is duff, it drops back to 100 Mb/s, (if it works at all).
Lastly, avoid a cable labelled as CCA, (or copper clad aluminium). It is rubbish and not up to the official standard. You want pure copper.
Hope that helps without getting too technical.
