Emacs has many settings which you can change. Most settings are customizable variables (see Variables), which are also called user options. There is a huge number of customizable variables, controlling numerous aspects of Emacs behavior; the variables documented in this manual are listed in Variable Index. A separate class of settings are the faces, which determine the fonts, colors, and other attributes of text (see Text Faces).
To browse and alter settings (both variables and faces), type M-x customize. This creates a customization buffer, which lets you navigate through a logically organized list of settings, edit and set their values, and save them permanently.