Its pretty straight forward, just make and account here imgur.com . Bring up the picture you want to use ,hit printscreen or ctrl C, go to your imgur page , hit ctrl V, image is uploaded and can be edited, or if you have the image on your PC already just drag n drop. You are then give 5 different types of links to use for different applications, use the 3rd to post in steem eg. HTML (website / blogs)