Both links work.
When you get to the new Forum page, do this:
1) Use the Sign Up button
Select the button and it will display the second screen ( 2 )
You can sign up in two ways. Sign up either by filling the form at 3 and pressing Create New Account
or by selecting ... with Google at 4
After you sign in, you can post a message
Use the circled button + New Topic
this screen where you write the topic (1); choose a category to post (usually this will be MIT App Inventor Help for most users)
Type your question in the 3 area. When done explaining the problem you need help with, press the blue Create Topic button ( 4 ).
Does this work for your?