The first number is the total number of times that that thread has been viewed (even if the forumer didn't make a post).

The second number is the number of posts for that thread.

The third (in brackets) is the number of new posts that you haven't read, so if you have never opened that thread yet the second and third number will be the same (eg. 10 posts in total, 10 to read)

If you have looked at that thread and then come back to it later and other people have posted meanwhile, the second and third number will be different (eg. 15 posts in total, 5 to read)

All clear, my dear?