We are at the moment in the process of installing a security certificate on this site. This takes 24hours to take effect, and meanwhile, users will be warned about the site having an insecure connection. Apologies about this - it will all be ironed out shortly, and the message will no longer appear!
To add a post - click on plus sign at top right (if it is not there, you are not signed in - see link at top of page). To later edit it, display the post, and click on pencil at top right.
If you wish to give somebody your contact details, you may prefer to do so by personal message (click on little envelope at top of page, then on plus sign) rather than putting it in a post which is visible to everyone.