Horizontal rule makes a horizontal line through your post like this:
Hide enclosed from suspicious users ~ dunno, eitger hides from search engine indexers (google, yahoo bots etc) or from users that Cloudflare doesnt like
Progress bar makes a progress bar.
[progress=25][/progress]
[progress=25][/progress]
Countdown - you set a date and time in it. It then displays how much time is left, when the set date/time passes, it displays what you put [countdown]here[/countdown].