You can add links and images from the tools on top of exercise editor box.
Adding a link to your exercise:
Copy the link you want to add. Click on the link icon and add your link to the url field. Change the text to display if you wish, and press OK.
Adding a picture to an exercise:
Click Attach an image on top of your exercise editor box.
Choose the image you want to add and click OK.
Adjust the image size from the image settings and press OK. The ideal image size is less than 600 px per side.