Click file and Print Layout to print multiple images to a page.

Thumbnails of available images appear on the left side.
(Available images are those images that you have opened.)
Drag the thumbnails to the "blank" page - workspace and click print.

Actual "print size"
This way you don't have to figure out the size. All you do is pick what to print and print it. Everything should print at the correct size.

If you want to add additional images, choose File Open Image, and choose the images.

(Only "image formats" (jpg, gif, png...) can be opened. E.g. you cannot import htm files.)

IMAGE DOES NOT FIT (Do you wish to scale it?)

I recommend you to always select NO.

Instead simply rotate it by using the "Rotate Counterclockwise 90" button. You'll find it on the toolbar, on my sample it's circled in red.

And then to center this image, just click on it, hold down the left mouse button and drag it towards the center (or where you want to have it).

You can also resize an image manually by dragging a corner handle.
This only works well if you need to make it smaller, because if you enlarge it, it will loose detail and sharpness.