Go to Image> Canvas size>

In the top box double the dimension, to increase canvas size to fit two images

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Make sure the Relative box is not ticked. Click the left hand middle arrow on the box with all the arrows. (This will make the canvas Wider with blank space on the right.

Open your second image. Then click Select> all> right click your mouse, highlight "copy" then release mouse button.

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Open original image. right click mouse and click "paste".

this will paste the image centrally on the canvas on top of the first image.

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Click Edit> free transform>. Your second image will now be selected and can be moved with the mouse into position next to the original. Giving you two images on one canvas.

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When happy with alignment click Layer> Flatten image> The image will now be one canvas with both images.

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Note.

In the step above where you clicked the middle left arrow this lets you select where to add the blank bit of canvas. (above, below, right or left or centrally)

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Anything not clear, just ask.

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Cheers

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Ron