Windows / Linux: Press Ctrl+K.
Mac: Press Cmd+K.
The Command Bar opens as a dialog with focus in the search field. You can start typing immediately. No need to click the Search button in the header. The shortcut is the fastest way.
Alternative: Click the Search button in the header (center, often with a "Search" label and Cmd+K hint). Same bar, same behavior.
Close: Press Escape or click outside the dialog. Your last search or selection can appear in Recent next time.
In Step 3 we will search for anything (posts, users, menu items, commands).