Adding a single image to a post or page on your WordPress site
First make sure you are logged in to your site, then start to edit the Post or Page you wish to add an image gallery to.
Click the 'Upload/Insert' link above the editing area.
If you want to upload new images, choose 'Select Files' from the 1st tab ('From Computer'). Your images will be uploaded.
Now click the 4th tab 'Media Library' and you will see all the photos you have available. Tick the box beside the ones you want to use in your gallery then click 'Attach all checked items to current post' (at the bottom)
Close the current dialogue box by clicking its X at top right. You will return to editing your post/page. Now scroll down to the area labelled 'File Gallery'.
You will see thumbnails of the photos you chose. Hover your mouse over the photo you want - a quadrant of options appears (see the diagram below). Tick the central box to choose the photo you want.
Make sure you have chosen the correct size of photo - thumbnail, medium, etc.
Click the 'Insert single files' button. The correct image HTML will be inserted into the post/page.
Click 'Update' as usual at top right of the editing page, then 'View post' to check on what you have done.
If you need to alter the image, delete the first one and repeat steps 6 onwards.