Hi Rick,
To associate an image to a post all you have to do is to attach an uploaded image within the post. To be more specific here's how:
Using Media Library (This assumes that you have already created the post):
1. Go to Media Library->Add New.
2. Browse and select your image file then Save all changes.
3. At the Media Library area, find your image then click the "attach" link at the "Attached to" column.
4. Find the Post where you like to attach the image. That's it. Your image is now attached to the post, and it will be used in the slider and as thumbnail.
Within Post:
1. Go to Edit Post or Create a New Post.
2. Select the image "Add an Image" located above the content area.
3. Browse and select your image file then Save all changes. That's it.
Hope this helps,
WPTD Webmaster