Press ⌘Space anywhere and a search box appears in the middle of the screen. Typing the first letters of an app's name and pressing ↩ opens it; that alone replaces the Start menu for most people within a day.
It also finds:
- Files, folders, emails, notes, contacts, calendar events, by name and by contents. ⌘↩ reveals a file in Finder instead of opening it.
- System Settings panes: type "bluetooth" or "wallpaper" and the pane opens.
- Sums and conversions:
18% of 240,72 f in c,120 usd in eur,3 miles in km. - Definitions, and web results when the search matches nothing local.
Arrow keys move through the results; the panel on the right previews the selected one. Esc clears the box, again closes it. If ⌘Space does nothing, another input method took it: System Settings → Keyboard → Keyboard Shortcuts → Spotlight.
The magnifying glass in the menu bar is the same thing for the mouse.