Pointers are just an index of the starts of sentences/paragraphs and it is used in nearly all occasions (some are fixed length but there are workarounds there, this is usually for menus though and even more rare is the end of section flag (here there is something the game parses and then starts a new line)). Typically they will be at the start of the text file or in a very similarly named file in the same directory, on rare occasions pointers can be in the binary (the ARM9 for the DS).
The will usually be a long string of numbers (you may have to flip them ABCD->DCBA or 0F76 -> 67F0) which may have "junk" between them (this junk can also be length of section, whether the text is bold/underlined or something like that).
When you change the length of the text naturally the pointer will now point to the wrong place.
Repointing is just changing the pointers to err point to the new position of the text.
There are several different styles of pointer, rather than type them out though (I am halfway through making a final version but have not done pointers yet) can I get you to go to the hacking docs:
(page search for "
pointers")
http://gbatemp.net/index.php?showtopic=73394
A simple example of plain pointers (linked in the topic):
http://gbatemp.net/index.php?showtopic=70192&st=41
The easiest way for me is to use a spreadsheet with hex capabilities (open office has hex2dec and the like built in and MS office if you add in the engineering pack has the option). Copy and paste the old pointer table (it will usually be simple enough to calculate so a list of where the pointers are can be useful) in along with the actual position of the original text to figure out how they match up (you might want to do a simple test).
Now you have the method the original pointers use you can reapply it to the edited text and get the new pointers.