Preferences is a menu with many options to control many parts of the system. To open it try
Preferences openFactoredPanel
or get one by way of Worldmenu - appearances... - preferences.
To read how to use the
panel (and how to make a preference be per-project):
Preferences giveHelpWithPreferences
This gives useful help, as does the balloonhelp on the options in Preferences. Even so, many of the preferences you can set will only start to get really meaningful when you know more about Squeak. Meanwhile, if you have a set-up of Squeak with preferences which satisfies you for the moment it is wise to save these with Save Current Settings as My Personal Preferences. For you can then return to those if later some preference was set with consequences you don't like.
Incidentally: Several things interact, such as your screen resolution and the apparent size of the letters on screen; and the fonts Squeak is running and what is set in Windows - appearances.. - systems fonts.