From the top-level customization buffer created by M-x customize, you can follow the links to the subgroups of the ‘Emacs’ customization group. These subgroups may contain settings for you to customize; they may also contain further subgroups, dealing with yet more specialized subsystems of Emacs. As you navigate the hierarchy of customization groups, you should find some settings that you want to customize.
If you are interested in customizing a particular setting or customization group, you can go straight there with the commands M-x customize-option, M-x customize-face, or M-x customize-group. See Specific Customization.
If you don't know exactly what groups or settings you want to customize, you can search for them using the editable search field at the top of each customization buffer. Here, you can type in a search term—either one or more words separated by spaces, or a regular expression (see Regexps). Then type <RET> in the field, or activate the ‘Search’ button next to it, to switch to a customization buffer containing groups and settings that match those terms. Note, however, that this feature only finds groups and settings that are loaded in the current Emacs session.
If you don't want customization buffers to show the search field,
change the variable
The command M-x customize-apropos is similar to using the search field, except that it reads the search term(s) using the minibuffer. See Specific Customization.
M-x customize-browse is another way to browse the available settings. This command creates a special customization buffer which shows only the names of groups and settings, in a structured layout. You can show the contents of a group, in the same buffer, by invoking the ‘[+]’ button next to the group name. When the group contents are shown, the button changes to ‘[-]’; invoking that hides the group contents again. Each group or setting in this buffer has a link which says ‘[Group]’, ‘[Option]’ or ‘[Face]’. Invoking this link creates an ordinary customization buffer showing just that group, option, or face; this is the way to change settings that you find with M-x customize-browse.