First you'll need to register and login (see instructions for that here).

Click on the "FORUM" link on the top navigation bar and then select the forum topic where you wish to make a post. On the bottom left hand corner you should see a button that says "New Topic". Click on this and you should now have a text window where you can write your post!

This text window has several toolbars that allow you to format your post and add links. When you have completed your post, click the "Preview" button located to the bottom right of the text window to preview your post and/or click "Save" to save your post.

If you want to edit or remove your post at a later date, you can do so by clicking on the "Edit" (a pencil) or "Remove" (a red "X") icons located at the top right-hand side of your post.