Here are some common keyboard shortcuts:

Command-H: Go to the Home screen.

Command-Space bar: Show or hide the Search field.

Command-Tab: Switch to the next most recently used app among your open apps.

Command-Shift-3: Take a screenshot.

Command-Shift-4: Take a screenshot and immediately open Markup to view or edit it.

Command-Option-D: Show or hide the Dock.

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Customize keyboard shortcuts

Open Settings, then tap Accessibility.

Tap Keyboards.

Tap Full Keyboard Access and turn it on.

Tap Commands.

Tap a command, then press a custom key combination to assign to it.

Tap Done.

Here is a Pro Tip I Found out. If u hold down the command button in any app u have open it will show a list of the commands.