After cutting up a pig (especially a big one), you are left with a lot of fat. Cut it up in cubes, approx. 2.5-3cm big. Or smaller, if you prefer, or if you still have the energy and time.
Put it in a big, preferably heavy-based, pot.
Have it on a very low heat.
Let it do its thing, stirring occasionally. Slowly it will start to melt. It should not bubble. The fat should just melt. It will take time, though.
This is what it looks like at the very end. You could eat the crunchy bits. They are like crackling. Or you could leave little bits in the lard pot (mixed in with the lard) - and spread it on bread, where the occasional crunchy bit is a treat.
The lard is poured into containers. Let it cool, put lid on. There you are.