How to add image into Custompress Custom Post

Maybe I am missing very obvious...

If I make a custom post and create a database of images and description text...where do I insert the image in the custom post? I know I could use the Advanced Custom Fields plugin and add an add image field, but from what I read in another forum I don't need to do that. Which field would the image go in from the Media Library? Would it be like a regular blog post where I would just throw the image in the regular content field and leave that as the only content in the field?

Thanks!