Go to the BST forum. You will see your avatar and a thread title line.
Select the dropdown arrow, and select a Tag for your thread - FS, FT, WTB, or FSOT
Fill out your thread title, and message description (Following the BST Guidelines sticky thread), and click "Post Thread"
To close your BST Thread and stop further comments:
You will see the three dots on the header of most web browsers and devices.
Click on that and select lock thread...this will close your BST thread.
Enjoy