The levels make sure you are learning the words and phrases in the most efficient way. We use a scientifically proven method called Spaced Repetition. All you have to remember is that the website will automatically calculate which is the best word or phrase to ask you next. The system ensures that you are gradually learning new words, that you get lots of revision of the most recent words or those words which you are having problems with, and that you are still revising old words.
Basically, the lower level a word is (level 0 is the lowest), the more often you will be asked it. The higher level a word is (level 10 is the highest), the less often you will be asked it. A word moves from level one (least well known) through to level ten (known extremely well). When you get a word right it moves up by one level, from say level two to level three. When you get a word wrong, it goes back to level zero. A level of -1 is used to indicate that a word has never been started.
In addition, the type of the question (multi-choice, Thai to English, or English to Thai) changes as the word or phrase moves through the levels.
The type of question asked (on the automatic question type) varies based on the level, and the timing of repetition is as follows:
Level 0, multi-choice, 1 minute
Level 1, multi-choice, 10 minutes
Level 2, multi-choice, 1 day
Level 3, multi-choice, 2 days
Level 4, Thai to English, 4 days
Level 5, Thai to English, 8 days
Level 6, Thai to English, 16 days
Level 7, English to Thai, 32 days (1 month)
Level 8, English to Thai, 64 days (2 months)
Level 9, English to Thai, 128 days (4 months)
Level 10, English to Thai, 256 days (8 months)
So, for example, if a word or phrase has been answered wrongly, it will go back to Level 0, and then be asked again after 1 minute of delay, as a multi-choice question. If the word or phrase is answered correctly, it will be asked again after 10 minutes, again as a multi-choice question. Note that the English to Thai phase of the learning only happens after 1 month of practise in the Thai to English mode. This ensures that you are thoroughly practised at hearing the word correctly (the listening phase), before you are required to be able to produce it yourself (the speaking phase).
See also the blog post New and radically improved algorithm for word and phrase teaching order announcing this.