This is a little tricky, and can require specialized materials, so be prepared to invest a little more money if you want to go long term and continue making your own soaps. For beginners, it is recommended you start by melting down pre-made bars of unscented soap. These are usually made specifically so you can customize the scent. Then, you just add some essential oils once the soap has been melted down, and let them set. If you want to go a step further, you can look up more intense and more time-consuming processes to make soap at home.
The most basic ingredients will be lye and some kind of fat or oil. That’s really all soap is, but with extra ingredients, you get the luxurious feels, foams, and scents of the higher end brands.