Visit the Learning WordPress Forum for additional info and to post questions
To edit and customize an existing WordPress post, login to your WordPress dashboard, and click the Posts menu.
Next, you will see all your posts in a menu like this one below:
Next, click the title of the post that you would like to edit and you will see a window like this one below. In this window, you can edit the title, edit the post content text, add an image in the content area and/or set a featured image (which will be used as your thumbnail image when the post is viewed in excerpt format). You can add the post to a category or create a new category etc.. When finished customizing the post to your liking click the ‘Update’ button on the right. View the finished post, and if necessary, repeat the same process until the post is what you want.