Go to the appropriate review forum. For example, if you saw an indy in Dallas, you would go to:
ECCIE Worldwide >
Texas >
Dallas Independent Provider Reviews-Dallas
Once there, just above the list of threads and even with the left border (where the "REPLY" button is where you're reading this post), you will see two buttons. One is labeled "NEW THREAD", the other "NEW REVIEW". Click on the "NEW REVIEW" button. A form will come up on your browser screen. Fill out the blanks and when you are done, you will see three buttons on the bottom ("Submit", "Preview", and "Cancel"). I'd suggest the Submit or Preview button.
(However, if you preview, don't forget to submit after previewing. As simple as it sounds, I've occasionally hit the wrong button (preview) and then close the window thinking that I've posted and wonder why my review didn't post.) So I just hit submit and then if it needs changing, click edit.
Welcome aboard and good luck.