Just press EDIT if all you want to do is change the text, then press PREVIEW and scroll down to make sure it's done what you wanted, then make sure you SAVE your changes.
To make a new line in the table, press EDIT, then copy the table line above and just change the text between the bars.
The little pictures are called:
The full list is here (thanks to Arthur and Nicola for making these!).
You'll see there are some notes below the edit box on how to edit wikis, and there are also links to more information if you want to do something more complicated.