Switch to manual focus if your camera has difficulty focusing a dim scene.
Or, if a scene has the same tone or color everywhere, as your camera may not be able to autofocus.
To focus manually, move the focus switch from A to M.
The switch is on, or near, the lens.
To focus, turn the lens focusing ring.
Don't turn the ring for zooming to focus the lens.
Nearly all beginning students confuse manual focus with manual exposure.
They're different.
Manual focus means you have to turn the lens manually to focus.
Manual exposure means you use the M exposure mode.