Hi, and welcome!
A "thread" is just a post with a list of replies to the same post. It's pretty simple--you will get the hang of it.
I'm sorry you are dealing with this situation. It is very scary to have a loved one stuck in an addiction. We have a "Friends and Family" forum for folks with a loved one with a substance abuse problem. If you go up to the top of the forum and click on the link that says "Sober Recovery : Alcoholism and Drug Addiction Help and Information," you will see a whole list of forums on the left. Scroll down until you see "Friends and Family" and underneath that you will see "Friends and Family of Substance Abusers."
There may not be a lot you can do to help your daughter until she wants help, but there is a lot you can do to help yourself (and the rest of the family).
Hugs,