Once you've logged into the blog, click the “Posts” link (1) in the left sidebar. When the “Posts” page appears (see screenshot below), click on “Add New”.
In the resulting “Add New Post” page, give your post a title in the title box (2), and then write away in the post box (3).
You can extend the size of the visible posting box by placing your cursor in the lower right corner (1), until it turns into a 2-headed arrow, then holding down the mouse button and dragging down.
If your post is supposed to be associated with a “category,” select it in the “Categories” box (2) in the right sidebar by clicking on the box next to the category name.
If you want your post to appear in the blog immediately, click on the “Publish” button (3) in the “Publish” box at the top of the right sidebar. If you want to save the post content to work on later, and do NOT want to publish it immediately, click on the “Save Draft” button (4). You can come back to it later.
If you published your post, you can see how it looks on the blog by clicking on the blog name text in the header at the top left of the screen. This will take you to the blog homepage and you can see your post.
If you didn't publish your post and want to see how it will look on the blog, click on the "Preview" button (to the right of "Save Draft").
To return to the Dashboard page, click on the “Site Admin” link (1) under “Welcome” in the sidebar.
If you need to make edits or you're ready to publish your post, read Editing and publishing saved posts.