I presume you mean the start menu and are you refering to the tiles, most used list, recently added list?
You can get all three back via start settings, simply ask Cortanat to search "start settings" and you can toggle them on and off.
If however you are refering to your app list then make sure you are not in tablet mode, to check click on the speech bubble next to the time / date and on the shortcut key that reads tablet mode click it so it's grey (off). This should revert you start menu to normal .
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