First you need to insert the image into your page or post. (View the adding images to pages and posts tutorial).
Once your image is in your post left click it (notice that after you left click the image you will see “handles” around it – this way you know you have selected your image):
Now click the “link” tool in your editor’s toolbar:
Paste the URL you want this picture to link to into the URL box. If you want the new page/website that you are linking to to open in another browser (recommended if you are sending someone away from your site using this link) then click the Open in new window option. If you want to link to content already on your site you can use the search tools to find it from this box and choose it (note – this is a new feature that is not as user friendly as we expect it will become over time).
Now click Update and you are returned to your page or post to finish it. Don’t forget to click Update or Publish to save your changes!