Here's a good tutorial.
https://ariel-square-four.blogspot.com/2014/02/cables-cable-making.html
I recommend bending double as many strands as possible, tuck and hammer them back in the nipple before final solder, even if the cavity is not a well like in the example above, but only a funnel/chamfer. I had a front brake nipple with a funnel/chamfer pulled off, in spite of spreading the end. A well is safer. Be thorough when doing this, it is important.
Be very very careful if using a open flame torch, the cable strands are thin and fries very rapidly, becomes blue or black and then the cable end and a bit above the nipple is ruined. The cable becomes Very fragile! Better to heat a chunk of copper or suitable material with the torch and use that for a soldering iron, if not a big enough soldering iron or electricity is available. Even a regular hot plate is usable, either directly solder on or adding heat to a solder iron tip-
For a soldering pot if you want that, a suitable small tin lid on a hot plate can be used.