If you have made for instance ten postings, then all of those postings list the number 10 in the post count. Once you make your another posting, all of you postings will carry the number 11.
In your case, you have made 26 postings when you wrote this, so your post count is set to 26. Once you make another posting your post count will go up by one again.
If I look at the posting I am replying to now, it reads 29 as a post count. This means that since you noticed the post count system you posted three more messages.
I hope the system is more clear now.