To bump your post, first you copy the address of that particular post (where to find it, is shown in post_address.jpg). Right click on it, and copy the address. Then you hit "New post" in the thread. Press that small piece of chain (shown in include_link.jpg, with orange arrow). Now you have to Paste the address of a post (I highlighted the whole link, so you can see, that it is between = and ]
Now, take a look at where I wrote "This is what others shall see". You can write anything here. For example, "bump".
The sentence bellow, marked by the green line shows you, how your posted message will look like.