First, I suggest you go into your User Control Panel and set your default viewing option to LINEAR, if it is not already. This will match what you were used to on the old board. You can play around with Threaded or Hybrid modes later when you're more familiar with the board. (Personally, although I understand all three modes, I still prefer linear.)
When you are looking at the bbs homepage and seeing the list of forums:
If you go to the LAST post, you will see only the last post, not the rest of the thread. For this reason, I seldom click that little arrow. But once there, to see the rest of the thread you can click your browser's BACK button to return to the bbs homepage, then click the thread title to go to the first unread message. This is a better choice, imho, than going to the last post in the first place.
My normal practice, however, is to just go to the forum. That way you can see ALL the threads easily, not just the one that received the most recent post.
When looking at the list of threads in a forum:
The same caveat applies about going to the last post in the thread.