There are three groups. All the groups contains 2000 words from the dictionary. The groups contain words that are common (group 1), less common (group 2) and uncommon (group 3). Click on all the words, that you know easily. If you just know them, after you read the translation, that means you don't memorize them yet by heart and therefore you shouldn't click them yet.
The resluts will be displayed after you finished the test. Please consider, that it's a rough estimation that is extrapolated by the answers you give here.
The words are selected randomly, so you can repeat the test as often as you like.