Making Cat5 Ethernet cables or repairing the ends is quite easy.
You will need a RJ45 connector, a crimper, and some strippers or a knife to strip the shield.
Strip the outer shield while taking care to not harm the wires.
Straighten all wires and untangle them.
Put the wires in the correct order, O, OW, GW, Blue, BlueW, G, BrnW, Brn.
Insert them into the connector with the tab facing down.
Check that the wires are in the correct order and fully into the connector.