A failed alignment
Sometimes the alignment fails. In that case, the resulting web page looks different:

The console header is red and there's also a red error message telling us that the alignment failed. The list of files comprises just two files: the HTML file and the "log.txt" file, wich actually contains the red error message in the console.
The HTML file contains an imperfect alignment, which you can correct manually, usually in a couple of minutes. You can either open the file immediately in the browser or download it and open it later. Note however that, in order to properly use the file, you need to be connected to the Internet when you load it in the browser.
The manual alignment
Let's open the HTML file:

Basically, there's a big table with two columns, with some instructions at the beginning and a big green button at the end.
Let's look more carefully at the first part:

First, the Celex code and the source and target languages are available in the top left corner.
Below them, there's a big backup "Save and continue" button. If you get tired of aligning you can click it to save your work in a new HTML file. You can reopen later that file to complete the alignment.
On the right side of the header you will find a description of the buttons and other functionalities useful during the alignment.
Then comes the table. There are two columns, for the source and target languages. A source language paragraph is automatically connected with the target language paragraph in the same row. You do not have to connect them one by one.

(These two segments are already connected to each other.)
Every paragraph has four buttons, which can be used to correct the alignment. Also, you can edit directly the text by clicking into a cell:

In certain cases, the paragraph is very long and doesn't fit completely in the cell. You can use the scrollbar to the right to view the entire text.

Now, let's see what those four buttons do.
Add a new paragraph
Suppose we have the following alignment:

You can see that the paragraph with the date is absent in the target language. You can fix that by adding a new paragraph below the first paragraph in the target language column. You add a new paragraph by clicking the green button in the cell above the insertion place. This will create a new cell with an editable text "<Add text here.>".

Then you edit the text as shown before and you're done.

Delete an existing paragraph
In some cases the alignment generates useless paragraphs, which you would rather delete.

To do that, click the second button (the red one). The buttons will change into a confirmation dialog:

If you press "Cancel", nothing will happen. If you press "Delete", the respective paragraph will be deleted:

Merging two paragraphs
In some cases two paragraphs should be combined into one paragraph. To do that, use the purple button in the first paragraph.

You are asked to confirm the action.
If you click "Cancel", nothing happens. If you click "Merge", the two paragraphs will be combined.

Splitting a paragraph
You may also need to split large paragraphs like in the following example.

The first source language paragraph actually contains two separate sentences and we need to split it in order to align the text with the target language text. To do that, we use the orange button. We click it once to expand the cell and see the entire text. You'll see that the button changes too.

Now use your mouse to click wherever you want to split the cell into two separate cells. You would probably split the paragraphs between the words "alike." and "Coordination". After clicking between those words, you get the following outcome:
