The process of making Ethernet lines is quite simple, given you have materials available. I have photo’s below of everything you need, minus the obvious (cable itself). Take a look at the photo’s– paying specific attention to the first photo with the multicolored wire, this is the order in which the small wires inside an Ethernet cable need to sit once slid into an RJ-45 connector (second photo).
First thing you will need to do is cut/peel back the outer layer of the cable, exposing the eight internal wires. The wires will be twisted into pairs (orange/white & orange, green/white & green, etc.) Untwist the pairs and straighten up the wires, then place them in the order from left to right, EXACTLY as in the first photo below. Once this is complete you will slide the RJ-45 plug (PIN SIDE UP) over the wires, making sure not to mix the wires. Look through the top of the plug to see if you can see all eight wires have filled the eight holes in the plug. If you are confident all wires are set and in order, next you will need the crimping tool just like the one in the last photo. Push your new RJ-45 end into the port on the crimping tool and crimp down until it completely releases. Finally you will cut the cable the length you need and repeat the steps for the other end.