Today, we call the gun powder made and used before the inception of the 20th century "black powder", mainly to distinguish it from modern gun powder that's mostly nitro based. The ingredients and methods for making black powder are readily available online and libraries around the globe. There is no reason to not talk about and fully understand what is black powder and the many ways it was and is produced.
BE AWARE OF YOUR LOCAL LAWS CONCERNING HAVING AND/OR MAKING AND STORING BLACK POWDER
Why make your own black powder? Availability is not easy these days and there is always the possibility it will cease to be sold. It will be lots cheaper to make good black powder considering its astronomically rising purchase pricing. Self sufficiency - if you have a flintlock gun, all you need is black powder, a rock to make sparks, and either some lead to cast a ball or if the gun is a smoothbore then something(s) to stuff down its barrel.
There are MANY online videos concerning making black powder. Here's one that I like ....
https://www.youtube.com/watch?v=7GQntdARoiw