Creating a New Post
From the Menu, under Posts, click on Add New.
Enter in a title for the post, and add the main body text.
Click on Publish. It will be to the right of the text editing area.
Editing a Post
From the Menu, under Posts, click on All Posts.
Find the post you wish to edit, and select Edit.
Make the changes you want, and then click Update. This button will be located in the same spot as the Publish button when you first wrote the post.
You can then click View Post to make sure the changes worked.