All posts should have an image unless they are very short bookmark posts that link to another article with a brief quote. Even bookmark posts can be improved with an image.
The best introductory series of posts for wordpress newbies is at learn.wordpress.com and they have a very good tutorial on working with images and video which will teach you the basics of the latest wordpress system.
This video runs through the same process although they are using a slightly older version of wordpress so they don’t have the new drag and drop technology. But it shows the basics of uploading an image and other media.
Once you master that have a look at the video below which shows you how to add a slideshow to wordpress. Slideshows are a good way to tell a simple story with five or six key images. The video below uses an older wordpress system but the basics are the same in wordpress 3.0. You can also add captions to each of your images once they are uploaded. Click on “show” in the image lists and then you will see a place to add in a caption. Keep captions at about 20 words and they will display nicely in a single line in the slideshow layout. As with all other parts of the system remember that when you add captions or complete a change or series of changes of any kind you must click on the save changes button in the dialogue box to activate your additions or changes.