As simple as ABC!
The level indicated for each activity (A1, B2 etc) corresponds to the Council of Europe Common Framework for language. In general terms, 

  • A1 or A2 is an elementary or false beginner level for learners with a very basic level of communication
  • B1 and B2 indicates learners who have reached a first level of autonomy in the language
  • C1 and C2 describes learners who can communicate in most situations but are less proficient than native speakers.
For more details about levels, click on the links below:
  • English version here
  • French version here