I'm assuming you're referring to rule 7:
'Don't bump your own threads unless it is a Help Request and it has been at least one week.'
^^ What that means is, say you start a thread off on one topic and no one responds to it, you cannot post in the same thread again until someone else responds. This is so we don't end up with threads entirely dominated by one member.
If the thread you've created is a help request, for example you want some advice because you think your computer may have some adware or malware, and no one responds, you may post in the thread a second time after a week of no replies.
You can reply to anyone in your threads at any time though.