Hi Sabrina,
When you open an exported TM in .txt format, you will see that the first part is a list of all fonts used during the translation process. After that section, you'll see the actual translation units. Here's what you'll see:
<TrU> (Translation Unit opening tag)
<CrD>23112007, 09:59:43 (creation date and time)
<CrU>SARA (name of person who created the segment)
<Seg L=EN-US>FALL (Source language: English from USA)
<Seg L=ES-EM>OTOÑO (Target language: Spanish International Sort)
</TrU> (Translation Unit closing tag)
This unit structure is repeated in the txt file.
To know the meaning for language codes, go to:
Workbench>Help>Help topics>Index
In the Index tab, write: codes in the export file
There will appear a list of codes.
Hope it helps!