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.
You can also click the Search button in the header (center, often with a "Search" label and Cmd+K hint). Same bar, same behavior.
Press Escape or click outside the dialog to close it. Your last search or selection can appear in Recent next time.
In Step 3 we will search for anything (posts, users, menu items, commands).