Working with the quote function.

Can someone explain to me how to work with the quote function because I can't figure it out.
Thanks in advance.

Besides the total "Quote" button [RH bottom of a post], you can select a part of the text [like I did above]. Over the highlighted text there appears a sort of balloon with the word 'quote'. If you click on that, a Reply window appears.
It should also be possible to break a large quote in parts, but I'm not that far advanced yet :)

If you want to reply with a quotation, click the ‘Quote’ button, not the ‘Reply’ button.
The editor window will open with the text of the post between two sets of square brackets.
If you want to edit the quotation, click in the right place in the text and make your changes.
Click immediately after the last square bracket and check that the cursor is flashing there.
Press return a time or two to give a bit of space below the quotation.
Type your reply.
Click on the ‘Post reply’ button.
All done!

Revisit the original text that’s in the background behind your composition window. You can highlight and quote individual passages to your heart's content.

As I did here:

Thanks everyone for an answer and help.