If to people are editing the same page at the same time their changes may conflict. If they do not conflict everything is fine. This wiki handles that automagically.
If two changes conflict the conflicting parts will be displayed on the page. You should correct it, because the other editor will not see a warning.
to be continued
The unix diff3 programm is used for that feature.
If diff3 cannot handle the problem by itself something like the following is displayed on the wiki page:
<<<<<<< you
lines you wrote
||||||| ancestor
the original lines
=======
lines the other person wrote
>>>>>>> other