First, to post you must be what is called a contributor. Before you can attain this exalted rank you must subscribe to the site. You can do this by looking down to the bottom right under Login where it says Register and click on the link. This will take you to the registration page. Immediately after you successfully complete the registration, you will be granted the rank of subscriber, which doesn’t let you do much more than read the site, which you can do without registering, edit your profile and submit comments on other posts. However, when I receive your registration, I can change your status to contributor, allowing you to post messages and longer articles to the site. I will make this change if you send an email to firstname.lastname@example.org requesting the change of status.
To post a message, simply login using the user name and password you chose when you registered. On the right, you will find the dashboard. Under Posts, click on the Add New button. This opens the Add New Post editing page. This page behaves much like a word processor, having a strip of editing buttons like any word processor. There are actually two editors, labeled Visual and HTML. Unless you like HTML coding, make sure the Visual tab is selected. Pause the mouse over any button and a call out will tell you what the button is for. Note particularly the link and unlink buttons. The link button will allow you to link to other sites or articles on the web that you would like to draw to the attention of other readers. The unlink button removes a selected link.
Clicking on the right-most button (the kitchen sink) will open a second row of buttons providing more editing options. I normally keep this “kitchen sink” row open all the time.
Now, simply type your message as you would with a word processor. If it is a long message or if you have to leave your computer before finishing, click on the Save Draft button at the right above. You can log out if necessary and log in later to finish the post. When the post is finished to your liking, click on the blue Submit for Review button. This will automatically send me an email informing me that your comment is awaiting review. I will review it and assuming there are no nasty personal attacks on me in the post, I will publish it. After you have made two “reviewed posts” to the site, all future posts will be published automatically.
I think you will find the process much easier than the length of this post implies. If you want more details, you can read all about posting at the WordPress Codex at this link.