Mrs Pea, I must admit I struggled with PIXresizer until I got the gist of how it works so I've just opened it but just forget working with one file or multiples for the moment.
Number 1 has a grey box which says load picture. Click on it and you'll see a box which says "Look in" (ignore what's showing in the box), click on the down arrow in the box and select pictures from the drop box which will show all your pic folders. Choose which folder your pic is in, click on the folder then select your pic. It helps if you've given your pic a title rather than having to scroll through whatever number your camera gave it. Double-click on the pic you want which will show in the right-hand window then select "Apply recommended." I created a folder for emailing my pics which should show in the top box which says Save in. Clkick on Save and it should be there in a format which you can email.