The most basic way of making soap from scratch is called "cold process" - because no heat is added to the soap during the process other than what is needed to melt the oils.
The first thing you'll need to start making soap is a recipe. Either get one from this site, a soap making book or Create Your Own Soap Recipe.
Next, assemble all of your equipment, materials and ingredients, your recipe, and organize your workspace.
Because it takes time to cool, make your lye solution first, and set it aside in a safe place.