I did it ! Thanks for the help guys.
I will show you the steps to do it, for YOU who are reading this :
1 - Open your web browser (Mozilla Firefox or Google Chrome)
2 - Go on the page where you need to find a variable text.
3 - Right click on the text, "Inspect the element" (FIRST SCREENSHOT)
4 - Go on the top of the HTML "block" (the last arrow which shows the bottom)
5 - Right click on the line with the arrow, and "Copy the exterior of the HTML"
6 - Come back on Zennoposter, click on the button on the top of Zennopoter's web browser (SECOND SCREENSHOT) (source: VladZen)
7 - Select "DOM-text" if unselected
8 - Click on "Copy to regex designer"
9 - Now the regex designer is opened. (THIRD SCREENSHOT)
10 - Paste the HTML in the box named "Before search text"
11 - At the end of the code you will have the variable text + the "end" code (</span></div> in this case)
Let's say you have APPLE BANANA<div>
Delete APPLE BANANA
12 - Take the end code that was after APPLE BANANA, cut it from "Before search text"
and paste it in "After search text" box
13 - Click on the checkboxes "Enable line breaks" and "Shortest match"
14 - Click on Test
15 - Now the result appeared on the right. Awesome !
Now you just have to copy the whole code in "Regular expression text" box and close the window
16 - In your Zennoposter project do a right click Tabs>Data
17 - Click on the checkbox "Parse result"
18 - Paste the code you copied on Regexp
19 - Choose a variable to save the result
20 - Annnd it's done ! WOOHOO you did it !
Now your bot is able to take text in an area no matter what it is (: .